Types in GTK+ / glib and (native) types in Raku

Below there is a table showing all kinds of type definitions used in the several layers C, Glib, GTK, Raku and the fundamental types defined in Gnome::GObject::Type called GType.

For sizes defined for C see also here. The next piece of C code from a glib file gtype.h shows te definition of a GType type. The Raku modules use the C libraries of Glib so we must use the gsize type.

/**
 * GType:
 *
 * A numerical value which represents the unique identifier of a registered
 * type.
 */
#if GLIB_SIZEOF_SIZE_T != GLIB_SIZEOF_LONG || !defined __cplusplus
typedef gsize                           GType;
#else   /* for historic reasons, C++ links against gulong GTypes */
typedef gulong                          GType;
#endif

So the table becomes like shown below;

① The fundamental GType names are needed when a sub can handle a scala of value types. For example the Gnome::Gtk3::TreeStore and Gnome::Gtk3::ListStore can handle columns of different types. The stores are initialized by defining a GType for each column and later a GValue wrapped into the Gnome::GObject::Value is used to set a value for a particular column and row.

② The boolean values can be given to native subs as True or False. These values are automatically unboxed into native integers when they are stored in a int32 type. When a native sub returns a boolean value, it cannot be coerced into a Bool typed variable automatically. One must call .Bool() on it to do so. Most of the time this is not necessary because the test control statements in perl handle 0 and !0 as False and True perfectly.

③ Raku sees an int as 64 bits when processor uses 64, 32 bits otherwise. However, in C the int is defined as a 32 bit type. Explanations on the internet varies here and there. This is confusing, so a decision is made to generate a type mapping in Gnome::N::GlibToRakuTypes distilled indirectly from the limits.h C include file, which takes these types into account and maps it to the Raku fixed ones. So gsize is mapped to uint64 and gint is mapped to int32. This also means that long and ulong are not used. See point ⑥.

Below is a type GEnum used from this mapping.

  sub gtk_window_set_gravity ( N-GObject $window, GEnum $gravity )
    is native(&gtk-lib)
    { * }

④ gint32/guint32 and gint64/guint64, although typedef’ed to int and long, are guaranteed to be 32 and 64 bits long according to the docs here.

⑤ Most enumerated values are generated automatically starting from 0. Sometimes these are flags, but still integer. When these are literal integer, the values are of type int. Raku will convert a enumeration name automatically to its integer value. The values are always returned as an int and must also be converted explicitly if you want to use the enumerated name of the integer. By the way, floating literals are double (num64), not float(num32)! Other types are not used in the GNOME libraries (I think).

⑥ Raku native types long, ulong are specific types of the Rakudo implementation.

⑦ Raku Int types can hold very large numbers. When used to set a smaller native integer, they are truncated to modulo the size of the type. For instance int8 is set modulo 256.