pub struct VariantType { /* private fields */ }
Expand description

Describes Variant types.

The Variant type system (based on the D-Bus one) describes types with “type strings”. VariantType is an owned immutable type string (you can think of it as a Box<str> statically guaranteed to be a valid type string), &VariantTy is a borrowed one (like &str). This section introduces the GVariant type system. It is based, in large part, on the D-Bus type system, with two major changes and some minor lifting of restrictions. The D-Bus specification, therefore, provides a significant amount of information that is useful when working with GVariant.

The first major change with respect to the D-Bus type system is the introduction of maybe (or “nullable”) types. Any type in GVariant can be converted to a maybe type, in which case, “nothing” (or “null”) becomes a valid value. Maybe types have been added by introducing the character “m” to type strings.

The second major change is that the GVariant type system supports the concept of “indefinite types” – types that are less specific than the normal types found in D-Bus. For example, it is possible to speak of “an array of any type” in GVariant, where the D-Bus type system would require you to speak of “an array of integers” or “an array of strings”. Indefinite types have been added by introducing the characters “*”, “?” and “r” to type strings.

Finally, all arbitrary restrictions relating to the complexity of types are lifted along with the restriction that dictionary entries may only appear nested inside of arrays.

Just as in D-Bus, GVariant types are described with strings (“type strings”). Subject to the differences mentioned above, these strings are of the same form as those found in D-Bus. Note, however: D-Bus always works in terms of messages and therefore individual type strings appear nowhere in its interface. Instead, “signatures” are a concatenation of the strings of the type of each argument in a message. GVariant deals with single values directly so GVariant type strings always describe the type of exactly one value. This means that a D-Bus signature string is generally not a valid GVariant type string – except in the case that it is the signature of a message containing exactly one argument.

An indefinite type is similar in spirit to what may be called an abstract type in other type systems. No value can exist that has an indefinite type as its type, but values can exist that have types that are subtypes of indefinite types. That is to say, Variant::type_() will never return an indefinite type, but calling [Variant::is_of_type()][crate::Variant::is_of_type()] with an indefinite type may return true. For example, you cannot have a value that represents “an array of no particular type”, but you can have an “array of integers” which certainly matches the type of “an array of no particular type”, since “array of integers” is a subtype of “array of no particular type”.

This is similar to how instances of abstract classes may not directly exist in other type systems, but instances of their non-abstract subtypes may. For example, in GTK, no object that has the type of GtkBin can exist (since GtkBin is an abstract class), but a GtkWindow can certainly be instantiated, and you would say that the GtkWindow is a GtkBin (since GtkWindow is a subclass of GtkBin).

GVariant Type Strings

A GVariant type string can be any of the following:

  • any basic type string (listed below)

  • “v”, “r” or “*”

  • one of the characters ‘a’ or ‘m’, followed by another type string

  • the character ‘(’, followed by a concatenation of zero or more other type strings, followed by the character ‘)’

  • the character ‘{’, followed by a basic type string (see below), followed by another type string, followed by the character ‘}’

A basic type string describes a basic type (as per [is_basic()][Self::is_basic()]) and is always a single character in length. The valid basic type strings are “b”, “y”, “n”, “q”, “i”, “u”, “x”, “t”, “h”, “d”, “s”, “o”, “g” and “?”.

The above definition is recursive to arbitrary depth. “aaaaai” and “(ui(nq((y)))s)” are both valid type strings, as is “a(aa(ui)(qna{ya(yd)}))”. In order to not hit memory limits, Variant imposes a limit on recursion depth of 65 nested containers. This is the limit in the D-Bus specification (64) plus one to allow a GDBusMessage to be nested in a top-level tuple.

The meaning of each of the characters is as follows:

  • b: the type string of G_VARIANT_TYPE_BOOLEAN; a boolean value.
  • y: the type string of G_VARIANT_TYPE_BYTE; a byte.
  • n: the type string of G_VARIANT_TYPE_INT16; a signed 16 bit integer.
  • q: the type string of G_VARIANT_TYPE_UINT16; an unsigned 16 bit integer.
  • i: the type string of G_VARIANT_TYPE_INT32; a signed 32 bit integer.
  • u: the type string of G_VARIANT_TYPE_UINT32; an unsigned 32 bit integer.
  • x: the type string of G_VARIANT_TYPE_INT64; a signed 64 bit integer.
  • t: the type string of G_VARIANT_TYPE_UINT64; an unsigned 64 bit integer.
  • h: the type string of G_VARIANT_TYPE_HANDLE; a signed 32 bit value that, by convention, is used as an index into an array of file descriptors that are sent alongside a D-Bus message.
  • d: the type string of G_VARIANT_TYPE_DOUBLE; a double precision floating point value.
  • s: the type string of G_VARIANT_TYPE_STRING; a string.
  • o: the type string of G_VARIANT_TYPE_OBJECT_PATH; a string in the form of a D-Bus object path.
  • g: the type string of G_VARIANT_TYPE_SIGNATURE; a string in the form of a D-Bus type signature.
  • ?: the type string of G_VARIANT_TYPE_BASIC; an indefinite type that is a supertype of any of the basic types.
  • v: the type string of G_VARIANT_TYPE_VARIANT; a container type that contain any other type of value.
  • a: used as a prefix on another type string to mean an array of that type; the type string “ai”, for example, is the type of an array of signed 32-bit integers.
  • m: used as a prefix on another type string to mean a “maybe”, or “nullable”, version of that type; the type string “ms”, for example, is the type of a value that maybe contains a string, or maybe contains nothing.
  • (): used to enclose zero or more other concatenated type strings to create a tuple type; the type string “(is)”, for example, is the type of a pair of an integer and a string.
  • r: the type string of G_VARIANT_TYPE_TUPLE; an indefinite type that is a supertype of any tuple type, regardless of the number of items.
  • {}: used to enclose a basic type string concatenated with another type string to create a dictionary entry type, which usually appears inside of an array to form a dictionary; the type string “a{sd}”, for example, is the type of a dictionary that maps strings to double precision floating point values.

The first type (the basic type) is the key type and the second type is the value type. The reason that the first type is restricted to being a basic type is so that it can easily be hashed.

  • *: the type string of G_VARIANT_TYPE_ANY; the indefinite type that is a supertype of all types. Note that, as with all type strings, this character represents exactly one type. It cannot be used inside of tuples to mean “any number of items”.

Any type string of a container that contains an indefinite type is, itself, an indefinite type. For example, the type string “a*” (corresponding to G_VARIANT_TYPE_ARRAY) is an indefinite type that is a supertype of every array type. “(*s)” is a supertype of all tuples that contain exactly two items where the second item is a string.

“a{?*}” is an indefinite type that is a supertype of all arrays containing dictionary entries where the key is any basic type and the value is any type at all. This is, by definition, a dictionary, so this type string corresponds to G_VARIANT_TYPE_DICTIONARY. Note that, due to the restriction that the key of a dictionary entry must be a basic type, “{**}” is not a valid type string.

Implementations

Tries to create a VariantType from a string slice.

Returns Ok if the string is a valid type string, Err otherwise. Creates a new VariantType corresponding to the type string given by type_string. It is appropriate to call g_variant_type_free() on the return value.

It is a programmer error to call this function with an invalid type string. Use [string_is_valid()][Self::string_is_valid()] if you are unsure.

type_string

a valid GVariant type string

Returns

a new VariantType

source

pub fn new_dict_entry(
    key_type: &VariantTy,
    value_type: &VariantTy
) -> VariantType

Creates a VariantType from a key and value type. Constructs the type corresponding to a dictionary entry with a key of type key and a value of type value.

It is appropriate to call g_variant_type_free() on the return value.

key

a basic VariantType

value

a VariantType

Returns

a new dictionary entry VariantType

Since 2.24

Creates a VariantType from an array element type. Constructs the type corresponding to an array of elements of the type type_.

It is appropriate to call g_variant_type_free() on the return value.

element

a VariantType

Returns

a new array VariantType

Since 2.24

Creates a VariantType from a maybe element type. Constructs the type corresponding to a maybe instance containing type type_ or Nothing.

It is appropriate to call g_variant_type_free() on the return value.

element

a VariantType

Returns

a new maybe VariantType

Since 2.24

Creates a VariantType from a maybe element type. Constructs a new tuple type, from items.

length is the number of items in items, or -1 to indicate that items is None-terminated.

It is appropriate to call g_variant_type_free() on the return value.

items

an array of GVariantTypes, one for each item

Returns

a new tuple VariantType

Since 2.24

Tries to create a VariantType from an owned string.

Returns Ok if the string is a valid type string, Err otherwise.

Methods from Deref<Target = VariantTy>

source

pub const DICT_ENTRY: &'static VariantTy = unsafe { VariantTy::from_str_unchecked(ffi::G_VARIANT_TYPE_DICT_ENTRY) }

Converts to a string slice.

Check if this variant type is a definite type.

Check if this variant type is a container type.

Check if this variant type is a basic type.

Check if this variant type is a maybe type.

Check if this variant type is an array type.

Check if this variant type is a tuple type.

source

pub fn is_dict_entry(&self) -> bool

Check if this variant type is a dict entry type.

Check if this variant type is a variant.

Check if this variant type is a subtype of another.

Return the element type of this variant type.

Panics

This function panics if not called with an array or maybe type.

Iterate over the types of this variant type.

Panics

This function panics if not called with a tuple or dictionary entry type.

Return the first type of this variant type.

Panics

This function panics if not called with a tuple or dictionary entry type.

Return the next type of this variant type.

Return the number of items in this variant type.

Return the key type of this variant type.

Panics

This function panics if not called with a dictionary entry type.

Return the value type of this variant type.

Panics

This function panics if not called with a dictionary entry type.

Trait Implementations

Converts this type into a shared reference of the (usually inferred) input type.

Immutably borrows from an owned value. Read more

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

The resulting type after dereferencing.

Dereferences the value.

Formats the value using the given formatter. Read more

Executes the destructor for this type. Read more

Converts to this type from the input type.

The associated error which can be returned from parsing.

Parses a string s to return a value of this type. Read more

Feeds this value into the given Hasher. Read more

Feeds a slice of this type into the given Hasher. Read more

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

Returns the type identifier of Self.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

Ensures that the type has been registered with the type system.

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

Uses borrowed data to replace owned data, usually by cloning. Read more

Returns a SendValue clone of self.

Converts the given value to a String. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.