Macro wrapper

macro_rules! wrapper {
    (
        $(#[$attr:meta])*
        $visibility:vis struct $name:ident $(<$($generic:ident $(: $bound:tt $(+ $bound2:tt)*)?),+>)? (Boxed<$ffi_name:ty>);

        match fn {
            copy => |$copy_arg:ident| $copy_expr:expr,
            free => |$free_arg:ident| $free_expr:expr,
            $(
            type_ => || $get_type_expr:expr,
            )?
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        $visibility:vis struct $name:ident $(<$($generic:ident $(: $bound:tt $(+ $bound2:tt)*)?),+>)? (BoxedInline<$ffi_name:ty>);

        match fn {
            $(
            copy => |$copy_arg:ident| $copy_expr:expr,
            free => |$free_arg:ident| $free_expr:expr,
            )?
            $(
            init => |$init_arg:ident| $init_expr:expr,
            copy_into => |$copy_into_arg_dest:ident, $copy_into_arg_src:ident| $copy_into_expr:expr,
            clear => |$clear_arg:ident| $clear_expr:expr,
            )?
            $(
            type_ => || $get_type_expr:expr,
            )?
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        $visibility:vis struct $name:ident $(<$($generic:ident $(: $bound:tt $(+ $bound2:tt)*)?),+>)? (BoxedInline<$ffi_name:ty>);
    ) => { ... };
    (
        $(#[$attr:meta])*
        $visibility:vis struct $name:ident $(<$($generic:ident $(: $bound:tt $(+ $bound2:tt)*)?),+>)? (Shared<$ffi_name:ty>);

        match fn {
            ref => |$ref_arg:ident| $ref_expr:expr,
            unref => |$unref_arg:ident| $unref_expr:expr,
            $(
            type_ => || $get_type_expr:expr,
            )?
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        $visibility:vis struct $name:ident $(<$($generic:ident $(: $bound:tt $(+ $bound2:tt)*)?),+>)? (Object<$ffi_name:ty $(, $ffi_class_name:ty)?>) $(@implements $($implements:path),+)?;

        match fn {
            type_ => || $get_type_expr:expr,
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        $visibility:vis struct $name:ident $(<$($generic:ident $(: $bound:tt $(+ $bound2:tt)*)?),+>)? (Object<$ffi_name:ty $(, $ffi_class_name:ty)?>) @extends $($extends:path),+ $(, @implements $($implements:path),+)?;

        match fn {
            type_ => || $get_type_expr:expr,
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        $visibility:vis struct $name:ident $(<$($generic:ident $(: $bound:tt $(+ $bound2:tt)*)?),+>)? (ObjectSubclass<$subclass:ty>) $(@implements $($implements:path),+)?;
    ) => { ... };
    (
        $(#[$attr:meta])*
        $visibility:vis struct $name:ident $(<$($generic:ident $(: $bound:tt $(+ $bound2:tt)*)?),+>)? (ObjectSubclass<$subclass:ty>) @extends $($extends:path),+ $(, @implements $($implements:path),+)?;
    ) => { ... };
    (
        $(#[$attr:meta])*
        $visibility:vis struct $name:ident $(<$($generic:ident $(: $bound:tt $(+ $bound2:tt)*)?),+>)? (Interface<$ffi_name:ty $(, $ffi_class_name:ty)?>) $(@requires $($requires:path),+)?;

        match fn {
            type_ => || $get_type_expr:expr,
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        $visibility:vis struct $name:ident $(<$($generic:ident $(: $bound:tt $(+ $bound2:tt)*)?),+>)? (ObjectInterface<$iface_name:ty>) $(@requires $($requires:path),+)?;
    ) => { ... };
}

Defines a wrapper type and implements the appropriate traits.

The basic syntax is

wrapper! {
    /// Your documentation goes here
    pub struct $name($kind<$foreign>);

    match fn {
        $fn_name => /* a closure-like expression */,
        ...
    }
}

This creates a wrapper named $name around the foreign type $foreign of $kind — one of Boxed, Shared, or Object.

Inside the match fn block there are closure-like expressions to provide ways of copying/freeing, or referencing/unreferencing the value that you are wrapping. These expressions will be evaluated in an unsafe context, since they frequently invoke extern functions from an FFI crate.

What follows is a description of each of the possible $kind: Boxed, Shared, and Object; note that each supports different sets of $fn_name inside the match fn block. Also, Object may require you to specify things like the class struct to wrap, plus any interfaces that the class implements.

Boxed (heap allocated)

Boxed records with single ownership allocated on the heap.

With no registered glib_ffi::GType:

wrapper! {
    /// Text buffer iterator
    pub struct TextIter(Boxed<ffi::GtkTextIter>);

    match fn {
        copy => |ptr| ffi::gtk_text_iter_copy(ptr),
        free => |ptr| ffi::gtk_text_iter_free(ptr),
    }
}

copy: |*const $foreign| -> *mut $foreign creates a copy of the value.

free: |*mut $foreign| frees the value.

With a registered glib_ffi::GType:

wrapper! {
    /// Text buffer iterator
    pub struct TextIter(Boxed<ffi::GtkTextIter>);

    match fn {
        copy     => |ptr| ffi::gtk_text_iter_copy(ptr),
        free     => |ptr| ffi::gtk_text_iter_free(ptr),
        type_ => ||    ffi::gtk_text_iter_get_type(),
    }
}

type_: || -> glib_ffi::GType (optional) returns the glib_ffi::GType that corresponds to the foreign struct.

BoxedInline (inline, stack allocated)

Boxed records with single ownership allocated on the stack or otherwise inline. With no registered glib_ffi::GType:

wrapper! {
    /// Text buffer iterator
    pub struct TextIter(BoxedInline<ffi::GtkTextIter>);

    match fn {
        copy => |ptr| ffi::gtk_text_iter_copy(ptr),
        free => |ptr| ffi::gtk_text_iter_free(ptr),
    }
}

copy: |*const $foreign| -> *mut $foreign (optional) creates a heap allocated copy of the value.

free: |*mut $foreign| (optional) frees the value.

With a registered glib_ffi::GType:

wrapper! {
    /// Text buffer iterator
    pub struct TextIter(BoxedInline<ffi::GtkTextIter>);

    match fn {
        copy     => |ptr| ffi::gtk_text_iter_copy(ptr),
        free     => |ptr| ffi::gtk_text_iter_free(ptr),
        type_ => ||    ffi::gtk_text_iter_get_type(),
    }
}

type_: || -> glib_ffi::GType (optional) returns the glib_ffi::GType that corresponds to the foreign struct.

Shared

Records with reference-counted, shared ownership.

With no registered glib_ffi::GType:

wrapper! {
    /// Object holding timing information for a single frame.
    pub struct FrameTimings(Shared<ffi::GdkFrameTimings>);

    match fn {
        ref   => |ptr| ffi::gdk_frame_timings_ref(ptr),
        unref => |ptr| ffi::gdk_frame_timings_unref(ptr),
    }
}

ref: |*mut $foreign| increases the refcount.

unref: |*mut $foreign| decreases the refcount.

With a registered glib_ffi::GType:

wrapper! {
    /// Object holding timing information for a single frame.
    pub struct FrameTimings(Shared<ffi::GdkFrameTimings>);

    match fn {
        ref      => |ptr| ffi::gdk_frame_timings_ref(ptr),
        unref    => |ptr| ffi::gdk_frame_timings_unref(ptr),
        type_ => ||    ffi::gdk_frame_timings_get_type(),
    }
}

type_: || -> glib_ffi::GType (optional) returns the glib_ffi::GType that corresponds to the foreign struct.

Object

Objects – classes. Note that the class name, if available, must be specified after the $foreign type; see below for non-derivable classes.

The basic syntax is this:

wrapper! {
    /// Your documentation goes here
    pub struct InstanceName(Object<ffi::InstanceStruct, ffi::ClassStruct>)
        @extends ParentClass, GrandparentClass, ...,
        @implements Interface1, Interface2, ...;

    match fn {
        type_ => || ffi::instance_get_type(),
    }
}

type_: || -> glib_ffi::GType returns the glib_ffi::GType that corresponds to the foreign class.

All parent classes must be specified

In the example above, “@extends ParentClass, GrandparentClass, ...,” is where you must specify all the parent classes of the one you are wrapping. The uppermost parent class, glib::Object, must not be specified.

For example, ffi::GtkWindowGroup derives directly from GObject, so it can be simply wrapped as follows:

wrapper! {
    pub struct WindowGroup(Object<ffi::GtkWindowGroup, ffi::GtkWindowGroupClass>);

    match fn {
        type_ => || ffi::gtk_window_group_get_type(),
    }
}

In contrast, ffi::GtkButton has a parent, grandparent, etc. classes, which must be specified:

wrapper! {
    pub struct Button(Object<ffi::GtkButton>) @extends Bin, Container, Widget;
        // see note on interfaces in the example below

    match fn {
        type_ => || ffi::gtk_button_get_type(),
    }
}

Objects which implement interfaces

The example above is incomplete, since ffi::GtkButton actually implements two interfaces, Buildable and Actionable. In this case, they must be specified after all the parent classes behind the @implements keyword:

wrapper! {
    pub struct Button(Object<ffi::GtkButton>)
        @extends Bin, Container, Widget, // parent classes
        @implements Buildable, Actionable;  // interfaces

    match fn {
        type_ => || ffi::gtk_button_get_type(),
    }
}

Non-derivable classes

By convention, GObject implements “final” classes, i.e. those who cannot be subclassed, by not exposing a public Class struct. This way it is not possible to override any methods, as there are no klass.method_name fields to overwrite. In this case, don’t specify a FFI class name at all in the Object<> part:

wrapper! {
    pub struct Clipboard(Object<ffi::GtkClipboard>);
    ...
}

Interfaces

Interfaces are passed in the same way to the macro but instead of specifying Object, Interface has to be specified:

wrapper! {
    pub struct TreeModel(Interface<ffi::GtkTreeModel, ffi::GtkTreeModelIface>);
    ...
}

Interfaces with prerequisites

Interfaces can declare prerequisites, i.e. the classes from which types that implement the interface have to inherit or interfaces that have to be implemented:

wrapper! {
    pub struct TreeSortable(Interface<ffi::GtkTreeSortable, ffi::GtkTreeSortable>) @requires TreeModel;
    ...
}