Macro glib::glib_wrapper

macro_rules! glib_wrapper {
    (
        $(#[$attr:meta])*
        pub struct $name:ident(Boxed<$ffi_name:path>);

        match fn {
            copy => |$copy_arg:ident| $copy_expr:expr,
            free => |$free_arg:ident| $free_expr:expr,
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        pub struct $name:ident(Boxed<$ffi_name:path>);

        match fn {
            copy => |$copy_arg:ident| $copy_expr:expr,
            free => |$free_arg:ident| $free_expr:expr,
            get_type => || $get_type_expr:expr,
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        pub struct $name:ident(Shared<$ffi_name:path>);

        match fn {
            ref => |$ref_arg:ident| $ref_expr:expr,
            unref => |$unref_arg:ident| $unref_expr:expr,
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        pub struct $name:ident(Shared<$ffi_name:path>);

        match fn {
            ref => |$ref_arg:ident| $ref_expr:expr,
            unref => |$unref_arg:ident| $unref_expr:expr,
            get_type => || $get_type_expr:expr,
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        pub struct $name:ident(Object<$ffi_name:path>);

        match fn {
            get_type => || $get_type_expr:expr,
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        pub struct $name:ident(Object<$ffi_name:path, $ffi_class_name:path>);

        match fn {
            get_type => || $get_type_expr:expr,
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        pub struct $name:ident(Object<$ffi_name:path>): [$($implements:tt)+];

        match fn {
            get_type => || $get_type_expr:expr,
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        pub struct $name:ident(Object<$ffi_name:path, $ffi_class_name:path>): [$($implements:tt)+];

        match fn {
            get_type => || $get_type_expr:expr,
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        pub struct $name:ident(Object<$ffi_name:path>): $($implements:path),+;

        match fn {
            get_type => || $get_type_expr:expr,
        }
    ) => { ... };
    (
        $(#[$attr:meta])*
        pub struct $name:ident(Object<$ffi_name:path, $ffi_class_name:path>): $($implements:path),+;

        match fn {
            get_type => || $get_type_expr:expr,
        }
    ) => { ... };
}

Defines a wrapper type and implements the appropriate traits.

The basic syntax is

glib_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

Boxed records with single ownership.

With no registered glib_ffi::GType:

glib_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:

glib_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),
        get_type => ||    ffi::gtk_text_iter_get_type(),
    }
}

get_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:

glib_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:

glib_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),
        get_type => ||    ffi::gdk_frame_timings_get_type(),
    }
}

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

Object

Objects -- classes and interfaces. 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:

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

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

get_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, "ParentClass, GrandparentClass, ...," is where you must specify all the parent classes of the one you are wrapping. It is not necessary to specify the uppermost GObject or GInitiallyUnowned parent classes.

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

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

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

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

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

    match fn {
        get_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:

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

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

Wrapping objects with parents/interfaces from different crates

Implementing types whose parents or interfaces come from different crates requires specifying the wrapped names of the parents/interfaces and their FFI counterparts as well. Note that these must be specified inside square brackets "[]", as comma-delimited pairs like "crate_name::WrappedName => ffi_crate_name::Name".

Here, note that the parent class for ffi::GtkApplication is gio::Application, which is the Rust wrapper for gio_ffi::GApplication. Similarly, the ActionGroup and ActionMap interfaces, and their corresponding ffi structs, come from different crates.

glib_wrapper! {
    pub struct Application(Object<ffi::GtkApplication, ffi::GtkApplicationClass>): [
        gio::Application => gio_ffi::GApplication,
        gio::ActionGroup => gio_ffi::GActionGroup,
        gio::ActionMap   => gio_ffi::GActionMap,
    ];

    match fn {
        get_type => || ffi::gtk_application_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 class name at all in the Object<> part:

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