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// Take a look at the license at the top of the repository in the LICENSE file.

//! `Variant` binding and helper traits.
//!
//! [`Variant`](struct.Variant.html) is an immutable dynamically-typed generic
//! container. Its type and value are defined at construction and never change.
//!
//! `Variant` types are described by [`VariantType`](../struct.VariantType.html)
//! "type strings".
//!
//! Although `GVariant` supports arbitrarily complex types, this binding is
//! currently limited to the basic ones: `bool`, `u8`, `i16`, `u16`, `i32`,
//! `u32`, `i64`, `u64`, `f64`, `&str`/`String`, and [`VariantDict`](../struct.VariantDict.html).
//!
//! # Examples
//!
//! ```
//! use glib::prelude::*; // or `use gtk::prelude::*;`
//! use glib::{Variant, FromVariant, ToVariant};
//! use std::collections::HashMap;
//!
//! // Using the `ToVariant` trait.
//! let num = 10.to_variant();
//!
//! // `is` tests the type of the value.
//! assert!(num.is::<i32>());
//!
//! // `get` tries to extract the value.
//! assert_eq!(num.get::<i32>(), Some(10));
//! assert_eq!(num.get::<u32>(), None);
//!
//! // `get_str` tries to borrow a string slice.
//! let hello = "Hello!".to_variant();
//! assert_eq!(hello.str(), Some("Hello!"));
//! assert_eq!(num.str(), None);
//!
//! // `bytes` tries to borrow a byte array (GVariant type `ay`),
//! // rather than creating a deep copy which would be expensive for
//! // nontrivially sized byte arrays.
//! // The test data here is the zstd compression header, which
//! // stands in for arbitrary binary data (e.g. not UTF-8).
//! let bufdata = b"\xFD\x2F\xB5\x28";
//! let bufv = bufdata.to_variant();
//! assert_eq!(bufv.bytes().unwrap(), bufdata);
//! assert!(num.bytes().is_err());
//!
//! // Variant carrying a Variant
//! let variant = Variant::from_variant(&hello);
//! let variant = variant.as_variant().unwrap();
//! assert_eq!(variant.str(), Some("Hello!"));
//!
//! // Variant carrying an array
//! let array = ["Hello".to_variant(), "there!".to_variant()];
//! let variant = Variant::from_array::<&str>(&array);
//! assert_eq!(variant.n_children(), 2);
//! assert_eq!(variant.child_value(0).str(), Some("Hello"));
//! assert_eq!(variant.child_value(1).str(), Some("there!"));
//!
//! // You can also convert from and to a Vec
//! let variant = vec!["Hello", "there!"].to_variant();
//! assert_eq!(variant.n_children(), 2);
//! let vec = <Vec<String>>::from_variant(&variant).unwrap();
//! assert_eq!(vec[0], "Hello");
//!
//! // Conversion to and from HashMap is also possible
//! let mut map: HashMap<u16, &str> = HashMap::new();
//! map.insert(1, "hi");
//! map.insert(2, "there");
//! let variant = map.to_variant();
//! assert_eq!(variant.n_children(), 2);
//! let map: HashMap<u16, String> = HashMap::from_variant(&variant).unwrap();
//! assert_eq!(map[&1], "hi");
//! assert_eq!(map[&2], "there");
//!
//! // And conversion to and from tuples.
//! let variant = ("hello", 42u16, vec![ "there", "you" ],).to_variant();
//! assert_eq!(variant.n_children(), 3);
//! assert_eq!(variant.type_().to_str(), "(sqas)");
//! let tuple = <(String, u16, Vec<String>)>::from_variant(&variant).unwrap();
//! assert_eq!(tuple.0, "hello");
//! assert_eq!(tuple.1, 42);
//! assert_eq!(tuple.2, &[ "there", "you"]);
//!
//! // `Option` is supported as well, through maybe types
//! let variant = Some("hello").to_variant();
//! assert_eq!(variant.n_children(), 1);
//! let mut s = <Option<String>>::from_variant(&variant).unwrap();
//! assert_eq!(s.unwrap(), "hello");
//! s = None;
//! let variant = s.to_variant();
//! assert_eq!(variant.n_children(), 0);
//! let s = <Option<String>>::from_variant(&variant).unwrap();
//! assert!(s.is_none());
//! ```

use crate::bytes::Bytes;
use crate::gstring::GString;
use crate::translate::*;
use crate::StaticType;
use crate::Type;
use crate::VariantTy;
use crate::VariantType;
use crate::{VariantIter, VariantStrIter};
use std::borrow::Cow;
use std::cmp::{Eq, Ordering, PartialEq, PartialOrd};
use std::collections::HashMap;
use std::fmt;
use std::hash::{BuildHasher, Hash, Hasher};
use std::slice;
use std::str;

wrapper! {
    /// A generic immutable value capable of carrying various types.
    ///
    /// See the [module documentation](index.html) for more details.
    // rustdoc-stripper-ignore-next-stop
    /// [`Variant`][crate::Variant] is a variant datatype; it can contain one or more values
    /// along with information about the type of the values.
    ///
    /// A [`Variant`][crate::Variant] may contain simple types, like an integer, or a boolean value;
    /// or complex types, like an array of two strings, or a dictionary of key
    /// value pairs. A [`Variant`][crate::Variant] is also immutable: once it's been created neither
    /// its type nor its content can be modified further.
    ///
    /// GVariant is useful whenever data needs to be serialized, for example when
    /// sending method parameters in D-Bus, or when saving settings using GSettings.
    ///
    /// When creating a new [`Variant`][crate::Variant], you pass the data you want to store in it
    /// along with a string representing the type of data you wish to pass to it.
    ///
    /// For instance, if you want to create a [`Variant`][crate::Variant] holding an integer value you
    /// can use:
    ///
    ///
    ///
    /// **⚠️ The following code is in C ⚠️**
    ///
    /// ```C
    ///   GVariant *v = g_variant_new ("u", 40);
    /// ```
    ///
    /// The string "u" in the first argument tells [`Variant`][crate::Variant] that the data passed to
    /// the constructor (40) is going to be an unsigned integer.
    ///
    /// More advanced examples of [`Variant`][crate::Variant] in use can be found in documentation for
    /// [GVariant format strings][gvariant-format-strings-pointers].
    ///
    /// The range of possible values is determined by the type.
    ///
    /// The type system used by [`Variant`][crate::Variant] is [`VariantType`][crate::VariantType].
    ///
    /// [`Variant`][crate::Variant] instances always have a type and a value (which are given
    /// at construction time). The type and value of a [`Variant`][crate::Variant] instance
    /// can never change other than by the [`Variant`][crate::Variant] itself being
    /// destroyed. A [`Variant`][crate::Variant] cannot contain a pointer.
    ///
    /// [`Variant`][crate::Variant] is reference counted using `g_variant_ref()` and
    /// `g_variant_unref()`. [`Variant`][crate::Variant] also has floating reference counts --
    /// see [`ref_sink()`][Self::ref_sink()].
    ///
    /// [`Variant`][crate::Variant] is completely threadsafe. A [`Variant`][crate::Variant] instance can be
    /// concurrently accessed in any way from any number of threads without
    /// problems.
    ///
    /// [`Variant`][crate::Variant] is heavily optimised for dealing with data in serialized
    /// form. It works particularly well with data located in memory-mapped
    /// files. It can perform nearly all deserialization operations in a
    /// small constant time, usually touching only a single memory page.
    /// Serialized [`Variant`][crate::Variant] data can also be sent over the network.
    ///
    /// [`Variant`][crate::Variant] is largely compatible with D-Bus. Almost all types of
    /// [`Variant`][crate::Variant] instances can be sent over D-Bus. See [`VariantType`][crate::VariantType] for
    /// exceptions. (However, [`Variant`][crate::Variant]'s serialization format is not the same
    /// as the serialization format of a D-Bus message body: use `GDBusMessage`,
    /// in the gio library, for those.)
    ///
    /// For space-efficiency, the [`Variant`][crate::Variant] serialization format does not
    /// automatically include the variant's length, type or endianness,
    /// which must either be implied from context (such as knowledge that a
    /// particular file format always contains a little-endian
    /// `G_VARIANT_TYPE_VARIANT` which occupies the whole length of the file)
    /// or supplied out-of-band (for instance, a length, type and/or endianness
    /// indicator could be placed at the beginning of a file, network message
    /// or network stream).
    ///
    /// A [`Variant`][crate::Variant]'s size is limited mainly by any lower level operating
    /// system constraints, such as the number of bits in `gsize`. For
    /// example, it is reasonable to have a 2GB file mapped into memory
    /// with `GMappedFile`, and call [`from_data()`][Self::from_data()] on it.
    ///
    /// For convenience to C programmers, [`Variant`][crate::Variant] features powerful
    /// varargs-based value construction and destruction. This feature is
    /// designed to be embedded in other libraries.
    ///
    /// There is a Python-inspired text language for describing [`Variant`][crate::Variant]
    /// values. [`Variant`][crate::Variant] includes a printer for this language and a parser
    /// with type inferencing.
    ///
    /// ## Memory Use
    ///
    /// [`Variant`][crate::Variant] tries to be quite efficient with respect to memory use.
    /// This section gives a rough idea of how much memory is used by the
    /// current implementation. The information here is subject to change
    /// in the future.
    ///
    /// The memory allocated by [`Variant`][crate::Variant] can be grouped into 4 broad
    /// purposes: memory for serialized data, memory for the type
    /// information cache, buffer management memory and memory for the
    /// [`Variant`][crate::Variant] structure itself.
    ///
    /// ## Serialized Data Memory
    ///
    /// This is the memory that is used for storing GVariant data in
    /// serialized form. This is what would be sent over the network or
    /// what would end up on disk, not counting any indicator of the
    /// endianness, or of the length or type of the top-level variant.
    ///
    /// The amount of memory required to store a boolean is 1 byte. 16,
    /// 32 and 64 bit integers and double precision floating point numbers
    /// use their "natural" size. Strings (including object path and
    /// signature strings) are stored with a nul terminator, and as such
    /// use the length of the string plus 1 byte.
    ///
    /// Maybe types use no space at all to represent the null value and
    /// use the same amount of space (sometimes plus one byte) as the
    /// equivalent non-maybe-typed value to represent the non-null case.
    ///
    /// Arrays use the amount of space required to store each of their
    /// members, concatenated. Additionally, if the items stored in an
    /// array are not of a fixed-size (ie: strings, other arrays, etc)
    /// then an additional framing offset is stored for each item. The
    /// size of this offset is either 1, 2 or 4 bytes depending on the
    /// overall size of the container. Additionally, extra padding bytes
    /// are added as required for alignment of child values.
    ///
    /// Tuples (including dictionary entries) use the amount of space
    /// required to store each of their members, concatenated, plus one
    /// framing offset (as per arrays) for each non-fixed-sized item in
    /// the tuple, except for the last one. Additionally, extra padding
    /// bytes are added as required for alignment of child values.
    ///
    /// Variants use the same amount of space as the item inside of the
    /// variant, plus 1 byte, plus the length of the type string for the
    /// item inside the variant.
    ///
    /// As an example, consider a dictionary mapping strings to variants.
    /// In the case that the dictionary is empty, 0 bytes are required for
    /// the serialization.
    ///
    /// If we add an item "width" that maps to the int32 value of 500 then
    /// we will use 4 byte to store the int32 (so 6 for the variant
    /// containing it) and 6 bytes for the string. The variant must be
    /// aligned to 8 after the 6 bytes of the string, so that's 2 extra
    /// bytes. 6 (string) + 2 (padding) + 6 (variant) is 14 bytes used
    /// for the dictionary entry. An additional 1 byte is added to the
    /// array as a framing offset making a total of 15 bytes.
    ///
    /// If we add another entry, "title" that maps to a nullable string
    /// that happens to have a value of null, then we use 0 bytes for the
    /// null value (and 3 bytes for the variant to contain it along with
    /// its type string) plus 6 bytes for the string. Again, we need 2
    /// padding bytes. That makes a total of 6 + 2 + 3 = 11 bytes.
    ///
    /// We now require extra padding between the two items in the array.
    /// After the 14 bytes of the first item, that's 2 bytes required.
    /// We now require 2 framing offsets for an extra two
    /// bytes. 14 + 2 + 11 + 2 = 29 bytes to encode the entire two-item
    /// dictionary.
    ///
    /// ## Type Information Cache
    ///
    /// For each GVariant type that currently exists in the program a type
    /// information structure is kept in the type information cache. The
    /// type information structure is required for rapid deserialization.
    ///
    /// Continuing with the above example, if a [`Variant`][crate::Variant] exists with the
    /// type "a{sv}" then a type information struct will exist for
    /// "a{sv}", "{sv}", "s", and "v". Multiple uses of the same type
    /// will share the same type information. Additionally, all
    /// single-digit types are stored in read-only static memory and do
    /// not contribute to the writable memory footprint of a program using
    /// [`Variant`][crate::Variant].
    ///
    /// Aside from the type information structures stored in read-only
    /// memory, there are two forms of type information. One is used for
    /// container types where there is a single element type: arrays and
    /// maybe types. The other is used for container types where there
    /// are multiple element types: tuples and dictionary entries.
    ///
    /// Array type info structures are 6 * sizeof (void *), plus the
    /// memory required to store the type string itself. This means that
    /// on 32-bit systems, the cache entry for "a{sv}" would require 30
    /// bytes of memory (plus malloc overhead).
    ///
    /// Tuple type info structures are 6 * sizeof (void *), plus 4 *
    /// sizeof (void *) for each item in the tuple, plus the memory
    /// required to store the type string itself. A 2-item tuple, for
    /// example, would have a type information structure that consumed
    /// writable memory in the size of 14 * sizeof (void *) (plus type
    /// string) This means that on 32-bit systems, the cache entry for
    /// "{sv}" would require 61 bytes of memory (plus malloc overhead).
    ///
    /// This means that in total, for our "a{sv}" example, 91 bytes of
    /// type information would be allocated.
    ///
    /// The type information cache, additionally, uses a `GHashTable` to
    /// store and look up the cached items and stores a pointer to this
    /// hash table in static storage. The hash table is freed when there
    /// are zero items in the type cache.
    ///
    /// Although these sizes may seem large it is important to remember
    /// that a program will probably only have a very small number of
    /// different types of values in it and that only one type information
    /// structure is required for many different values of the same type.
    ///
    /// ## Buffer Management Memory
    ///
    /// [`Variant`][crate::Variant] uses an internal buffer management structure to deal
    /// with the various different possible sources of serialized data
    /// that it uses. The buffer is responsible for ensuring that the
    /// correct call is made when the data is no longer in use by
    /// [`Variant`][crate::Variant]. This may involve a `g_free()` or a `g_slice_free()` or
    /// even `g_mapped_file_unref()`.
    ///
    /// One buffer management structure is used for each chunk of
    /// serialized data. The size of the buffer management structure
    /// is 4 * (void *). On 32-bit systems, that's 16 bytes.
    ///
    /// ## GVariant structure
    ///
    /// The size of a [`Variant`][crate::Variant] structure is 6 * (void *). On 32-bit
    /// systems, that's 24 bytes.
    ///
    /// [`Variant`][crate::Variant] structures only exist if they are explicitly created
    /// with API calls. For example, if a [`Variant`][crate::Variant] is constructed out of
    /// serialized data for the example given above (with the dictionary)
    /// then although there are 9 individual values that comprise the
    /// entire dictionary (two keys, two values, two variants containing
    /// the values, two dictionary entries, plus the dictionary itself),
    /// only 1 [`Variant`][crate::Variant] instance exists -- the one referring to the
    /// dictionary.
    ///
    /// If calls are made to start accessing the other values then
    /// [`Variant`][crate::Variant] instances will exist for those values only for as long
    /// as they are in use (ie: until you call `g_variant_unref()`). The
    /// type information is shared. The serialized data and the buffer
    /// management structure for that serialized data is shared by the
    /// child.
    ///
    /// ## Summary
    ///
    /// To put the entire example together, for our dictionary mapping
    /// strings to variants (with two entries, as given above), we are
    /// using 91 bytes of memory for type information, 29 bytes of memory
    /// for the serialized data, 16 bytes for buffer management and 24
    /// bytes for the [`Variant`][crate::Variant] instance, or a total of 160 bytes, plus
    /// malloc overhead. If we were to use [`child_value()`][Self::child_value()] to
    /// access the two dictionary entries, we would use an additional 48
    /// bytes. If we were to have other dictionaries of the same type, we
    /// would use more memory for the serialized data and buffer
    /// management for those dictionaries, but the type information would
    /// be shared.
    #[doc(alias = "GVariant")]
    pub struct Variant(Shared<ffi::GVariant>);

    match fn {
        ref => |ptr| ffi::g_variant_ref_sink(ptr),
        unref => |ptr| ffi::g_variant_unref(ptr),
    }
}

impl StaticType for Variant {
    fn static_type() -> Type {
        Type::VARIANT
    }
}

#[doc(hidden)]
impl crate::value::ValueType for Variant {
    type Type = Variant;
}

#[doc(hidden)]
unsafe impl<'a> crate::value::FromValue<'a> for Variant {
    type Checker = crate::value::GenericValueTypeOrNoneChecker<Self>;

    unsafe fn from_value(value: &'a crate::Value) -> Self {
        let ptr = gobject_ffi::g_value_dup_variant(value.to_glib_none().0);
        assert!(!ptr.is_null());
        from_glib_full(ptr)
    }
}

#[doc(hidden)]
impl crate::value::ToValue for Variant {
    fn to_value(&self) -> crate::Value {
        unsafe {
            let mut value = crate::Value::from_type(Variant::static_type());
            gobject_ffi::g_value_take_variant(
                value.to_glib_none_mut().0,
                self.to_glib_full() as *mut _,
            );
            value
        }
    }

    fn value_type(&self) -> crate::Type {
        Variant::static_type()
    }
}

#[doc(hidden)]
impl crate::value::ToValueOptional for Variant {
    fn to_value_optional(s: Option<&Self>) -> crate::Value {
        let mut value = crate::Value::for_value_type::<Self>();
        unsafe {
            gobject_ffi::g_value_take_variant(
                value.to_glib_none_mut().0,
                s.to_glib_full() as *mut _,
            );
        }

        value
    }
}

/// An error returned from the [`try_get`](struct.Variant.html#method.try_get) function
/// on a [`Variant`](struct.Variant.html) when the expected type does not match the actual type.
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct VariantTypeMismatchError {
    pub actual: VariantType,
    pub expected: VariantType,
}

impl VariantTypeMismatchError {
    pub fn new(actual: VariantType, expected: VariantType) -> Self {
        Self { actual, expected }
    }
}

impl fmt::Display for VariantTypeMismatchError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "Type mismatch: Expected '{}' got '{}'",
            self.expected, self.actual
        )
    }
}

impl std::error::Error for VariantTypeMismatchError {}

impl Variant {
    /// Returns the type of the value.
    // rustdoc-stripper-ignore-next-stop
    /// Determines the type of `self`.
    ///
    /// The return value is valid for the lifetime of `self` and must not
    /// be freed.
    ///
    /// # Returns
    ///
    /// a [`VariantType`][crate::VariantType]
    pub fn type_(&self) -> &VariantTy {
        unsafe { VariantTy::from_ptr(ffi::g_variant_get_type(self.to_glib_none().0)) }
    }

    /// Returns `true` if the type of the value corresponds to `T`.
    #[inline]
    pub fn is<T: StaticVariantType>(&self) -> bool {
        self.type_() == T::static_variant_type()
    }

    /// Tries to extract a value of type `T`.
    ///
    /// Returns `Some` if `T` matches the variant's type.
    // rustdoc-stripper-ignore-next-stop
    /// Deconstructs a [`Variant`][crate::Variant] instance.
    ///
    /// Think of this function as an analogue to `scanf()`.
    ///
    /// The arguments that are expected by this function are entirely
    /// determined by `format_string`. `format_string` also restricts the
    /// permissible types of `self`. It is an error to give a value with
    /// an incompatible type. See the section on
    /// [GVariant format strings][gvariant-format-strings].
    /// Please note that the syntax of the format string is very likely to be
    /// extended in the future.
    ///
    /// `format_string` determines the C types that are used for unpacking
    /// the values and also determines if the values are copied or borrowed,
    /// see the section on
    /// [GVariant format strings][gvariant-format-strings-pointers].
    /// ## `format_string`
    /// a [`Variant`][crate::Variant] format string
    #[inline]
    pub fn get<T: FromVariant>(&self) -> Option<T> {
        T::from_variant(self)
    }

    /// Tries to extract a value of type `T`.
    pub fn try_get<T: FromVariant>(&self) -> Result<T, VariantTypeMismatchError> {
        self.get().ok_or_else(|| {
            VariantTypeMismatchError::new(
                self.type_().to_owned(),
                T::static_variant_type().into_owned(),
            )
        })
    }

    /// Boxes value.
    #[inline]
    pub fn from_variant(value: &Variant) -> Self {
        unsafe { from_glib_none(ffi::g_variant_new_variant(value.to_glib_none().0)) }
    }

    /// Unboxes self.
    ///
    /// Returns `Some` if self contains a `Variant`.
    #[inline]
    #[doc(alias = "get_variant")]
    pub fn as_variant(&self) -> Option<Variant> {
        unsafe { from_glib_full(ffi::g_variant_get_variant(self.to_glib_none().0)) }
    }

    /// Reads a child item out of a container `Variant` instance.
    ///
    /// # Panics
    ///
    /// * if `self` is not a container type.
    /// * if given `index` is larger than number of children.
    // rustdoc-stripper-ignore-next-stop
    /// Reads a child item out of a container [`Variant`][crate::Variant] instance. This
    /// includes variants, maybes, arrays, tuples and dictionary
    /// entries. It is an error to call this function on any other type of
    /// [`Variant`][crate::Variant].
    ///
    /// It is an error if `index_` is greater than the number of child items
    /// in the container. See [`n_children()`][Self::n_children()].
    ///
    /// The returned value is never floating. You should free it with
    /// `g_variant_unref()` when you're done with it.
    ///
    /// Note that values borrowed from the returned child are not guaranteed to
    /// still be valid after the child is freed even if you still hold a reference
    /// to `self`, if `self` has not been serialized at the time this function is
    /// called. To avoid this, you can serialize `self` by calling
    /// [`data()`][Self::data()] and optionally ignoring the return value.
    ///
    /// There may be implementation specific restrictions on deeply nested values,
    /// which would result in the unit tuple being returned as the child value,
    /// instead of further nested children. [`Variant`][crate::Variant] is guaranteed to handle
    /// nesting up to at least 64 levels.
    ///
    /// This function is O(1).
    /// ## `index_`
    /// the index of the child to fetch
    ///
    /// # Returns
    ///
    /// the child at the specified index
    #[doc(alias = "get_child_value")]
    #[doc(alias = "g_variant_get_child_value")]
    pub fn child_value(&self, index: usize) -> Variant {
        assert!(self.is_container());
        assert!(index < self.n_children());

        unsafe { from_glib_full(ffi::g_variant_get_child_value(self.to_glib_none().0, index)) }
    }

    /// Try to read a child item out of a container `Variant` instance.
    ///
    /// It returns `None` if `self` is not a container type or if the given
    /// `index` is larger than number of children.
    pub fn try_child_value(&self, index: usize) -> Option<Variant> {
        if !(self.is_container() && index < self.n_children()) {
            return None;
        }

        let v =
            unsafe { from_glib_full(ffi::g_variant_get_child_value(self.to_glib_none().0, index)) };
        Some(v)
    }

    /// Try to read a child item out of a container `Variant` instance.
    ///
    /// It returns `Ok(None)` if `self` is not a container type or if the given
    /// `index` is larger than number of children.  An error is thrown if the
    /// type does not match.
    pub fn try_child_get<T: StaticVariantType + FromVariant>(
        &self,
        index: usize,
    ) -> Result<Option<T>, VariantTypeMismatchError> {
        // TODO: In the future optimize this by using g_variant_get_child()
        // directly to avoid allocating a GVariant.
        self.try_child_value(index).map(|v| v.try_get()).transpose()
    }

    /// Read a child item out of a container `Variant` instance.
    ///
    /// # Panics
    ///
    /// * if `self` is not a container type.
    /// * if given `index` is larger than number of children.
    /// * if the expected variant type does not match
    pub fn child_get<T: StaticVariantType + FromVariant>(&self, index: usize) -> T {
        // TODO: In the future optimize this by using g_variant_get_child()
        // directly to avoid allocating a GVariant.
        self.child_value(index).get().unwrap()
    }

    /// Tries to extract a `&str`.
    ///
    /// Returns `Some` if the variant has a string type (`s`, `o` or `g` type
    /// strings).
    #[doc(alias = "get_str")]
    #[doc(alias = "g_variant_get_string")]
    pub fn str(&self) -> Option<&str> {
        unsafe {
            match self.type_().to_str() {
                "s" | "o" | "g" => {
                    let mut len = 0;
                    let ptr = ffi::g_variant_get_string(self.to_glib_none().0, &mut len);
                    let ret = str::from_utf8_unchecked(slice::from_raw_parts(
                        ptr as *const u8,
                        len as usize,
                    ));
                    Some(ret)
                }
                _ => None,
            }
        }
    }

    /// Tries to extract a `&[u8]` from a variant of type `ay` (array of bytes).
    ///
    /// Returns an error if the type is not `ay`.
    pub fn bytes(&self) -> Result<&[u8], VariantTypeMismatchError> {
        unsafe {
            let t = self.type_();
            let expected_ty = &*Vec::<u8>::static_variant_type();
            if t == expected_ty {
                let selfv = self.to_glib_none();
                let len = ffi::g_variant_get_size(selfv.0);
                let ptr = ffi::g_variant_get_data(selfv.0);
                let ret = slice::from_raw_parts(ptr as *const u8, len as usize);
                Ok(ret)
            } else {
                Err(VariantTypeMismatchError {
                    actual: t.to_owned(),
                    expected: expected_ty.to_owned(),
                })
            }
        }
    }

    /// Creates a new GVariant array from children.
    ///
    /// All children must be of type `T`.
    pub fn from_array<T: StaticVariantType>(children: &[Variant]) -> Self {
        let type_ = T::static_variant_type();

        for child in children {
            assert_eq!(type_, child.type_());
        }
        unsafe {
            from_glib_none(ffi::g_variant_new_array(
                type_.as_ptr() as *const _,
                children.to_glib_none().0,
                children.len(),
            ))
        }
    }

    /// Creates a new GVariant tuple from children.
    pub fn from_tuple(children: &[Variant]) -> Self {
        unsafe {
            from_glib_none(ffi::g_variant_new_tuple(
                children.to_glib_none().0,
                children.len(),
            ))
        }
    }

    /// Creates a new maybe Variant.
    pub fn from_maybe<T: StaticVariantType>(child: Option<&Variant>) -> Self {
        let type_ = T::static_variant_type();
        let ptr = match child {
            Some(child) => {
                assert_eq!(type_, child.type_());

                child.to_glib_none().0
            }
            None => std::ptr::null(),
        };
        unsafe {
            from_glib_none(ffi::g_variant_new_maybe(
                type_.as_ptr() as *const _,
                ptr as *mut ffi::GVariant,
            ))
        }
    }

    /// Constructs a new serialised-mode GVariant instance.
    // rustdoc-stripper-ignore-next-stop
    /// Constructs a new serialized-mode [`Variant`][crate::Variant] instance. This is the
    /// inner interface for creation of new serialized values that gets
    /// called from various functions in gvariant.c.
    ///
    /// A reference is taken on `bytes`.
    ///
    /// The data in `bytes` must be aligned appropriately for the `type_` being loaded.
    /// Otherwise this function will internally create a copy of the memory (since
    /// GLib 2.60) or (in older versions) fail and exit the process.
    /// ## `type_`
    /// a [`VariantType`][crate::VariantType]
    /// ## `bytes`
    /// a [`Bytes`][crate::Bytes]
    /// ## `trusted`
    /// if the contents of `bytes` are trusted
    ///
    /// # Returns
    ///
    /// a new [`Variant`][crate::Variant] with a floating reference
    #[doc(alias = "g_variant_new_from_bytes")]
    pub fn from_bytes<T: StaticVariantType>(bytes: &Bytes) -> Self {
        unsafe {
            from_glib_none(ffi::g_variant_new_from_bytes(
                T::static_variant_type().as_ptr() as *const _,
                bytes.to_glib_none().0,
                false.into_glib(),
            ))
        }
    }

    /// Constructs a new serialised-mode GVariant instance.
    ///
    /// This is the same as `from_bytes`, except that checks on the passed
    /// data are skipped.
    ///
    /// You should not use this function on data from external sources.
    ///
    /// # Safety
    ///
    /// Since the data is not validated, this is potentially dangerous if called
    /// on bytes which are not guaranteed to have come from serialising another
    /// Variant.  The caller is responsible for ensuring bad data is not passed in.
    pub unsafe fn from_bytes_trusted<T: StaticVariantType>(bytes: &Bytes) -> Self {
        from_glib_none(ffi::g_variant_new_from_bytes(
            T::static_variant_type().as_ptr() as *const _,
            bytes.to_glib_none().0,
            true.into_glib(),
        ))
    }

    /// Returns the serialised form of a GVariant instance.
    // rustdoc-stripper-ignore-next-stop
    /// Returns a pointer to the serialized form of a [`Variant`][crate::Variant] instance.
    /// The semantics of this function are exactly the same as
    /// [`data()`][Self::data()], except that the returned [`Bytes`][crate::Bytes] holds
    /// a reference to the variant data.
    ///
    /// # Returns
    ///
    /// A new [`Bytes`][crate::Bytes] representing the variant data
    #[doc(alias = "get_data_as_bytes")]
    #[doc(alias = "g_variant_get_data_as_bytes")]
    pub fn data_as_bytes(&self) -> Bytes {
        unsafe { from_glib_full(ffi::g_variant_get_data_as_bytes(self.to_glib_none().0)) }
    }

    /// Returns a copy of the variant in normal form.
    // rustdoc-stripper-ignore-next-stop
    /// Gets a [`Variant`][crate::Variant] instance that has the same value as `self` and is
    /// trusted to be in normal form.
    ///
    /// If `self` is already trusted to be in normal form then a new
    /// reference to `self` is returned.
    ///
    /// If `self` is not already trusted, then it is scanned to check if it
    /// is in normal form. If it is found to be in normal form then it is
    /// marked as trusted and a new reference to it is returned.
    ///
    /// If `self` is found not to be in normal form then a new trusted
    /// [`Variant`][crate::Variant] is created with the same value as `self`.
    ///
    /// It makes sense to call this function if you've received [`Variant`][crate::Variant]
    /// data from untrusted sources and you want to ensure your serialized
    /// output is definitely in normal form.
    ///
    /// If `self` is already in normal form, a new reference will be returned
    /// (which will be floating if `self` is floating). If it is not in normal form,
    /// the newly created [`Variant`][crate::Variant] will be returned with a single non-floating
    /// reference. Typically, `g_variant_take_ref()` should be called on the return
    /// value from this function to guarantee ownership of a single non-floating
    /// reference to it.
    ///
    /// # Returns
    ///
    /// a trusted [`Variant`][crate::Variant]
    #[doc(alias = "g_variant_get_normal_form")]
    pub fn normal_form(&self) -> Self {
        unsafe { from_glib_full(ffi::g_variant_get_normal_form(self.to_glib_none().0)) }
    }

    /// Returns a copy of the variant in the opposite endianness.
    // rustdoc-stripper-ignore-next-stop
    /// Performs a byteswapping operation on the contents of `self`. The
    /// result is that all multi-byte numeric data contained in `self` is
    /// byteswapped. That includes 16, 32, and 64bit signed and unsigned
    /// integers as well as file handles and double precision floating point
    /// values.
    ///
    /// This function is an identity mapping on any value that does not
    /// contain multi-byte numeric data. That include strings, booleans,
    /// bytes and containers containing only these things (recursively).
    ///
    /// The returned value is always in normal form and is marked as trusted.
    ///
    /// # Returns
    ///
    /// the byteswapped form of `self`
    #[doc(alias = "g_variant_byteswap")]
    pub fn byteswap(&self) -> Self {
        unsafe { from_glib_full(ffi::g_variant_byteswap(self.to_glib_none().0)) }
    }

    /// Determines the number of children in a container GVariant instance.
    // rustdoc-stripper-ignore-next-stop
    /// Determines the number of children in a container [`Variant`][crate::Variant] instance.
    /// This includes variants, maybes, arrays, tuples and dictionary
    /// entries. It is an error to call this function on any other type of
    /// [`Variant`][crate::Variant].
    ///
    /// For variants, the return value is always 1. For values with maybe
    /// types, it is always zero or one. For arrays, it is the length of the
    /// array. For tuples it is the number of tuple items (which depends
    /// only on the type). For dictionary entries, it is always 2
    ///
    /// This function is O(1).
    ///
    /// # Returns
    ///
    /// the number of children in the container
    #[doc(alias = "g_variant_n_children")]
    pub fn n_children(&self) -> usize {
        assert!(self.is_container());

        unsafe { ffi::g_variant_n_children(self.to_glib_none().0) }
    }

    /// Create an iterator over items in the variant.
    ///
    /// Note that this heap allocates a variant for each element,
    /// which can be particularly expensive for large arrays.
    pub fn iter(&self) -> VariantIter {
        assert!(self.is_container());

        VariantIter::new(self.clone())
    }

    /// Create an iterator over borrowed strings from a GVariant of type `as` (array of string).
    ///
    /// This will fail if the variant is not an array of with
    /// the expected child type.
    ///
    /// A benefit of this API over [`Self::iter()`] is that it
    /// minimizes allocation, and provides strongly typed access.
    ///
    /// ```
    /// # use glib::prelude::*;
    /// let strs = &["foo", "bar"];
    /// let strs_variant: glib::Variant = strs.to_variant();
    /// for s in strs_variant.array_iter_str()? {
    ///     println!("{}", s);
    /// }
    /// # Ok::<(), Box<dyn std::error::Error>>(())
    /// ```
    pub fn array_iter_str(&self) -> Result<VariantStrIter, VariantTypeMismatchError> {
        let child_ty = String::static_variant_type();
        let actual_ty = self.type_();
        let expected_ty = child_ty.with_array();
        if actual_ty != expected_ty {
            return Err(VariantTypeMismatchError {
                actual: actual_ty.to_owned(),
                expected: expected_ty,
            });
        }

        Ok(VariantStrIter::new(self))
    }

    /// Variant has a container type.
    // rustdoc-stripper-ignore-next-stop
    /// Checks if `self` is a container.
    ///
    /// # Returns
    ///
    /// [`true`] if `self` is a container
    #[doc(alias = "g_variant_is_container")]
    pub fn is_container(&self) -> bool {
        unsafe { ffi::g_variant_is_container(self.to_glib_none().0) != ffi::GFALSE }
    }
}

unsafe impl Send for Variant {}
unsafe impl Sync for Variant {}

impl fmt::Debug for Variant {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Variant")
            .field("ptr", &self.to_glib_none().0)
            .field("type", &self.type_())
            .field("value", &self.to_string())
            .finish()
    }
}

impl fmt::Display for Variant {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let serialized: GString = unsafe {
            from_glib_full(ffi::g_variant_print(
                self.to_glib_none().0,
                false.into_glib(),
            ))
        };
        f.write_str(&serialized)
    }
}

impl PartialEq for Variant {
    #[doc(alias = "g_variant_equal")]
    fn eq(&self, other: &Self) -> bool {
        unsafe {
            from_glib(ffi::g_variant_equal(
                self.to_glib_none().0 as *const _,
                other.to_glib_none().0 as *const _,
            ))
        }
    }
}

impl Eq for Variant {}

impl PartialOrd for Variant {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        unsafe {
            if ffi::g_variant_classify(self.to_glib_none().0)
                != ffi::g_variant_classify(other.to_glib_none().0)
            {
                return None;
            }

            if self.is_container() {
                return None;
            }

            let res = ffi::g_variant_compare(
                self.to_glib_none().0 as *const _,
                other.to_glib_none().0 as *const _,
            );

            Some(res.cmp(&0))
        }
    }
}

impl Hash for Variant {
    #[doc(alias = "g_variant_hash")]
    fn hash<H: Hasher>(&self, state: &mut H) {
        unsafe { state.write_u32(ffi::g_variant_hash(self.to_glib_none().0 as *const _)) }
    }
}

/// Converts to `Variant`.
pub trait ToVariant {
    /// Returns a `Variant` clone of `self`.
    fn to_variant(&self) -> Variant;
}

/// Extracts a value.
pub trait FromVariant: Sized + StaticVariantType {
    /// Tries to extract a value.
    ///
    /// Returns `Some` if the variant's type matches `Self`.
    fn from_variant(variant: &Variant) -> Option<Self>;
}

/// Returns `VariantType` of `Self`.
pub trait StaticVariantType {
    /// Returns the `VariantType` corresponding to `Self`.
    fn static_variant_type() -> Cow<'static, VariantTy>;
}

impl StaticVariantType for Variant {
    fn static_variant_type() -> Cow<'static, VariantTy> {
        unsafe { VariantTy::from_str_unchecked("v").into() }
    }
}

impl<'a, T: ?Sized + ToVariant> ToVariant for &'a T {
    fn to_variant(&self) -> Variant {
        <T as ToVariant>::to_variant(self)
    }
}

impl<'a, T: ?Sized + StaticVariantType> StaticVariantType for &'a T {
    fn static_variant_type() -> Cow<'static, VariantTy> {
        <T as StaticVariantType>::static_variant_type()
    }
}

macro_rules! impl_numeric {
    ($name:ty, $type_str:expr, $new_fn:ident, $get_fn:ident) => {
        impl StaticVariantType for $name {
            fn static_variant_type() -> Cow<'static, VariantTy> {
                unsafe { VariantTy::from_str_unchecked($type_str).into() }
            }
        }

        impl ToVariant for $name {
            fn to_variant(&self) -> Variant {
                unsafe { from_glib_none(ffi::$new_fn(*self)) }
            }
        }

        impl FromVariant for $name {
            fn from_variant(variant: &Variant) -> Option<Self> {
                unsafe {
                    if variant.is::<Self>() {
                        Some(ffi::$get_fn(variant.to_glib_none().0))
                    } else {
                        None
                    }
                }
            }
        }
    };
}

impl_numeric!(u8, "y", g_variant_new_byte, g_variant_get_byte);
impl_numeric!(i16, "n", g_variant_new_int16, g_variant_get_int16);
impl_numeric!(u16, "q", g_variant_new_uint16, g_variant_get_uint16);
impl_numeric!(i32, "i", g_variant_new_int32, g_variant_get_int32);
impl_numeric!(u32, "u", g_variant_new_uint32, g_variant_get_uint32);
impl_numeric!(i64, "x", g_variant_new_int64, g_variant_get_int64);
impl_numeric!(u64, "t", g_variant_new_uint64, g_variant_get_uint64);
impl_numeric!(f64, "d", g_variant_new_double, g_variant_get_double);

impl StaticVariantType for bool {
    fn static_variant_type() -> Cow<'static, VariantTy> {
        unsafe { VariantTy::from_str_unchecked("b").into() }
    }
}

impl ToVariant for bool {
    fn to_variant(&self) -> Variant {
        unsafe { from_glib_none(ffi::g_variant_new_boolean(self.into_glib())) }
    }
}

impl FromVariant for bool {
    fn from_variant(variant: &Variant) -> Option<Self> {
        unsafe {
            if variant.is::<Self>() {
                Some(from_glib(ffi::g_variant_get_boolean(
                    variant.to_glib_none().0,
                )))
            } else {
                None
            }
        }
    }
}

impl StaticVariantType for String {
    fn static_variant_type() -> Cow<'static, VariantTy> {
        unsafe { VariantTy::from_str_unchecked("s").into() }
    }
}

impl ToVariant for String {
    fn to_variant(&self) -> Variant {
        self[..].to_variant()
    }
}

impl FromVariant for String {
    fn from_variant(variant: &Variant) -> Option<Self> {
        variant.str().map(String::from)
    }
}

impl StaticVariantType for str {
    fn static_variant_type() -> Cow<'static, VariantTy> {
        unsafe { VariantTy::from_str_unchecked("s").into() }
    }
}

impl ToVariant for str {
    fn to_variant(&self) -> Variant {
        unsafe { from_glib_none(ffi::g_variant_new_take_string(self.to_glib_full())) }
    }
}

impl<T: StaticVariantType> StaticVariantType for Option<T> {
    fn static_variant_type() -> Cow<'static, VariantTy> {
        let child_type = T::static_variant_type();
        let signature = format!("m{}", child_type.to_str());

        VariantType::new(&signature)
            .expect("incorrect signature")
            .into()
    }
}

impl<T: StaticVariantType + ToVariant> ToVariant for Option<T> {
    fn to_variant(&self) -> Variant {
        Variant::from_maybe::<T>(self.as_ref().map(|m| m.to_variant()).as_ref())
    }
}

impl<T: StaticVariantType + FromVariant> FromVariant for Option<T> {
    fn from_variant(variant: &Variant) -> Option<Self> {
        unsafe {
            if variant.is::<Self>() {
                let c_child = ffi::g_variant_get_maybe(variant.to_glib_none().0);
                if !c_child.is_null() {
                    let child: Variant = from_glib_full(c_child);

                    Some(T::from_variant(&child))
                } else {
                    Some(None)
                }
            } else {
                None
            }
        }
    }
}

impl<T: StaticVariantType> StaticVariantType for [T] {
    fn static_variant_type() -> Cow<'static, VariantTy> {
        T::static_variant_type().with_array().into()
    }
}

impl<T: StaticVariantType + ToVariant> ToVariant for [T] {
    fn to_variant(&self) -> Variant {
        let mut vec = Vec::with_capacity(self.len());
        for child in self {
            vec.push(child.to_variant());
        }
        Variant::from_array::<T>(&vec)
    }
}

impl<T: FromVariant> FromVariant for Vec<T> {
    fn from_variant(variant: &Variant) -> Option<Self> {
        if !variant.is_container() {
            return None;
        }

        let mut vec = Vec::with_capacity(variant.n_children());

        for i in 0..variant.n_children() {
            match variant.child_value(i).get() {
                Some(child) => vec.push(child),
                None => return None,
            }
        }

        Some(vec)
    }
}

impl<T: StaticVariantType + ToVariant> ToVariant for Vec<T> {
    fn to_variant(&self) -> Variant {
        let mut vec = Vec::with_capacity(self.len());
        for child in self {
            vec.push(child.to_variant());
        }
        Variant::from_array::<T>(&vec)
    }
}

impl<T: StaticVariantType> StaticVariantType for Vec<T> {
    fn static_variant_type() -> Cow<'static, VariantTy> {
        <[T]>::static_variant_type()
    }
}

#[test]
fn test_regression_from_variant_panics() {
    let variant = "text".to_variant();
    let hashmap: Option<HashMap<u64, u64>> = FromVariant::from_variant(&variant);
    assert!(hashmap.is_none());

    let variant = HashMap::<u64, u64>::new().to_variant();
    let hashmap: Option<HashMap<u64, u64>> = FromVariant::from_variant(&variant);
    assert!(hashmap.is_some());
}

impl<K, V, H> FromVariant for HashMap<K, V, H>
where
    K: FromVariant + Eq + Hash,
    V: FromVariant,
    H: BuildHasher + Default,
{
    fn from_variant(variant: &Variant) -> Option<Self> {
        if !variant.is_container() {
            return None;
        }

        let mut map = HashMap::default();

        for i in 0..variant.n_children() {
            let entry = variant.child_value(i);
            let key = match entry.child_value(0).get() {
                Some(key) => key,
                None => return None,
            };
            let val = match entry.child_value(1).get() {
                Some(val) => val,
                None => return None,
            };

            map.insert(key, val);
        }

        Some(map)
    }
}

impl<K, V> ToVariant for HashMap<K, V>
where
    K: StaticVariantType + ToVariant + Eq + Hash,
    V: StaticVariantType + ToVariant,
{
    fn to_variant(&self) -> Variant {
        let mut vec = Vec::with_capacity(self.len());
        for (key, value) in self {
            let entry = DictEntry::new(key, value).to_variant();
            vec.push(entry);
        }
        Variant::from_array::<DictEntry<K, V>>(&vec)
    }
}

/// A Dictionary entry.
///
/// While GVariant format allows a dictionary entry to be an independent type, typically you'll need
/// to use this in a dictionary, which is simply an array of dictionary entries. The following code
/// creates a dictionary:
///
/// ```
///# use glib::prelude::*; // or `use gtk::prelude::*;`
/// use glib::{Variant, FromVariant, ToVariant};
/// use glib::variant::DictEntry;
///
/// let entries = vec![
///     DictEntry::new("uuid", 1000u32).to_variant(),
///     DictEntry::new("guid", 1001u32).to_variant(),
/// ];
/// let dict = Variant::from_array::<DictEntry<&str, u32>>(&entries);
/// assert_eq!(dict.n_children(), 2);
/// assert_eq!(dict.type_().to_str(), "a{su}");
/// ```
pub struct DictEntry<K, V> {
    key: K,
    value: V,
}

impl<K, V> DictEntry<K, V>
where
    K: StaticVariantType + ToVariant + Eq + Hash,
    V: StaticVariantType + ToVariant,
{
    pub fn new(key: K, value: V) -> Self {
        Self { key, value }
    }

    pub fn key(&self) -> &K {
        &self.key
    }

    pub fn value(&self) -> &V {
        &self.value
    }
}

impl<K, V> FromVariant for DictEntry<K, V>
where
    K: FromVariant + Eq + Hash,
    V: FromVariant,
{
    fn from_variant(variant: &Variant) -> Option<Self> {
        let key = match variant.child_value(0).get() {
            Some(key) => key,
            None => return None,
        };
        let value = match variant.child_value(1).get() {
            Some(value) => value,
            None => return None,
        };

        Some(Self { key, value })
    }
}

impl<K, V> ToVariant for DictEntry<K, V>
where
    K: StaticVariantType + ToVariant + Eq + Hash,
    V: StaticVariantType + ToVariant,
{
    fn to_variant(&self) -> Variant {
        unsafe {
            from_glib_none(ffi::g_variant_new_dict_entry(
                self.key.to_variant().to_glib_none().0,
                self.value.to_variant().to_glib_none().0,
            ))
        }
    }
}

impl ToVariant for Variant {
    fn to_variant(&self) -> Variant {
        Variant::from_variant(self)
    }
}

impl FromVariant for Variant {
    fn from_variant(variant: &Variant) -> Option<Self> {
        variant.as_variant()
    }
}

impl<K: StaticVariantType, V: StaticVariantType> StaticVariantType for DictEntry<K, V> {
    fn static_variant_type() -> Cow<'static, VariantTy> {
        let key_type = K::static_variant_type();
        let value_type = V::static_variant_type();
        let signature = format!("{{{}{}}}", key_type.to_str(), value_type.to_str());

        VariantType::new(&signature)
            .expect("incorrect signature")
            .into()
    }
}

impl<K, V, H> StaticVariantType for HashMap<K, V, H>
where
    K: StaticVariantType,
    V: StaticVariantType,
    H: BuildHasher + Default,
{
    fn static_variant_type() -> Cow<'static, VariantTy> {
        let key_type = K::static_variant_type();
        let value_type = V::static_variant_type();
        let signature = format!("a{{{}{}}}", key_type.to_str(), value_type.to_str());

        VariantType::new(&signature)
            .expect("incorrect signature")
            .into()
    }
}

macro_rules! tuple_impls {
    ($($len:expr => ($($n:tt $name:ident)+))+) => {
        $(
            impl<$($name),+> StaticVariantType for ($($name,)+)
            where
                $($name: StaticVariantType,)+
            {
                fn static_variant_type() -> Cow<'static, VariantTy> {
                    let mut signature = String::with_capacity(255);
                    signature.push('(');
                    $(
                        signature.push_str($name::static_variant_type().to_str());
                    )+
                    signature.push(')');

                    VariantType::new(&signature).expect("incorrect signature").into()
                }
            }

            impl<$($name),+> FromVariant for ($($name,)+)
            where
                $($name: FromVariant,)+
            {
                fn from_variant(variant: &Variant) -> Option<Self> {
                    Some((
                        $(
                            match $name::from_variant(&variant.child_value($n)) {
                                Some(field) => field,
                                None => return None,
                            },
                        )+
                    ))
                }
            }

            impl<$($name),+> ToVariant for ($($name,)+)
            where
                $($name: ToVariant,)+
            {
                fn to_variant(&self) -> Variant {
                    let mut fields = Vec::with_capacity($len);
                    $(
                        let field = self.$n.to_variant();
                        fields.push(field);
                    )+
                    Variant::from_tuple(&fields)
                }
            }
        )+
    }
}

tuple_impls! {
    1 => (0 T0)
    2 => (0 T0 1 T1)
    3 => (0 T0 1 T1 2 T2)
    4 => (0 T0 1 T1 2 T2 3 T3)
    5 => (0 T0 1 T1 2 T2 3 T3 4 T4)
    6 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5)
    7 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6)
    8 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7)
    9 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8)
    10 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9)
    11 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10)
    12 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11)
    13 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12)
    14 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12 13 T13)
    15 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12 13 T13 14 T14)
    16 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12 13 T13 14 T14 15 T15)
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::collections::{HashMap, HashSet};

    macro_rules! unsigned {
        ($name:ident, $ty:ident) => {
            #[test]
            fn $name() {
                let mut n = $ty::max_value();
                while n > 0 {
                    let v = n.to_variant();
                    assert_eq!(v.get(), Some(n));
                    n /= 2;
                }
            }
        };
    }

    macro_rules! signed {
        ($name:ident, $ty:ident) => {
            #[test]
            fn $name() {
                let mut n = $ty::max_value();
                while n > 0 {
                    let v = n.to_variant();
                    assert_eq!(v.get(), Some(n));
                    let v = (-n).to_variant();
                    assert_eq!(v.get(), Some(-n));
                    n /= 2;
                }
            }
        };
    }

    unsigned!(test_u8, u8);
    unsigned!(test_u16, u16);
    unsigned!(test_u32, u32);
    unsigned!(test_u64, u64);
    signed!(test_i16, i16);
    signed!(test_i32, i32);
    signed!(test_i64, i64);

    #[test]
    fn test_str() {
        let s = "this is a test";
        let v = s.to_variant();
        assert_eq!(v.str(), Some(s));
        assert_eq!(42u32.to_variant().str(), None);
    }

    #[test]
    fn test_bytes() {
        let b = b"this is a test";
        let v = b.to_variant();
        assert_eq!(v.bytes().unwrap(), b);
        assert!(42u32.to_variant().bytes().is_err());
    }

    #[test]
    fn test_string() {
        let s = String::from("this is a test");
        let v = s.to_variant();
        assert_eq!(v.get(), Some(s));
        assert_eq!(v.normal_form(), v);
    }

    #[test]
    fn test_eq() {
        let v1 = "this is a test".to_variant();
        let v2 = "this is a test".to_variant();
        let v3 = "test".to_variant();
        assert_eq!(v1, v2);
        assert_ne!(v1, v3);
    }

    #[test]
    fn test_hash() {
        let v1 = "this is a test".to_variant();
        let v2 = "this is a test".to_variant();
        let v3 = "test".to_variant();
        let mut set = HashSet::new();
        set.insert(v1);
        assert!(set.contains(&v2));
        assert!(!set.contains(&v3));

        assert_eq!(
            <HashMap<&str, (&str, u8, u32)>>::static_variant_type().to_str(),
            "a{s(syu)}"
        );
    }

    #[test]
    fn test_array() {
        assert_eq!(<Vec<&str>>::static_variant_type().to_str(), "as");
        assert_eq!(
            <Vec<(&str, u8, u32)>>::static_variant_type().to_str(),
            "a(syu)"
        );
        let a = ["foo", "bar", "baz"].to_variant();
        assert_eq!(a.normal_form(), a);
        assert_eq!(a.array_iter_str().unwrap().len(), 3);
        let o = 0u32.to_variant();
        assert!(o.array_iter_str().is_err());
    }

    #[test]
    fn test_get() -> Result<(), Box<dyn std::error::Error>> {
        let u = 42u32.to_variant();
        assert!(u.get::<i32>().is_none());
        assert_eq!(u.get::<u32>().unwrap(), 42);
        assert!(u.try_get::<i32>().is_err());
        // Test ? conversion
        assert_eq!(u.try_get::<u32>()?, 42);
        Ok(())
    }

    #[test]
    fn test_byteswap() {
        let u = 42u32.to_variant();
        assert_eq!(u.byteswap().get::<u32>().unwrap(), 704643072u32);
        assert_eq!(u.byteswap().byteswap().get::<u32>().unwrap(), 42u32);
    }

    #[test]
    fn test_try_child() {
        let a = ["foo"].to_variant();
        assert!(a.try_child_value(0).is_some());
        assert_eq!(a.try_child_get::<String>(0).unwrap().unwrap(), "foo");
        assert_eq!(a.child_get::<String>(0), "foo");
        assert!(a.try_child_get::<u32>(0).is_err());
        assert!(a.try_child_value(1).is_none());
        assert!(a.try_child_get::<String>(1).unwrap().is_none());
        let u = 42u32.to_variant();
        assert!(u.try_child_value(0).is_none());
        assert!(u.try_child_get::<String>(0).unwrap().is_none());
    }
}