Ensures that the indicated
type has been registered with the
type system, and its _class_init() method has been run.
In theory, simply calling the type’s _get_type() method (or using
the corresponding macro) is supposed take care of this. However,
_get_type() methods are often marked
G_GNUC_CONST for performance
reasons, even though this is technically incorrect (since
G_GNUC_CONST requires that the function not have side effects,
which _get_type() methods do on the first call). As a result, if
you write a bare call to a _get_type() macro, it may get optimized
out by the compiler. Using
g_type_ensure() guarantees that the
type’s _get_type() method is called.