Fiddle::Pointer#free=

static VALUE
rb_fiddle_ptr_free_set(VALUE self, VALUE val)
{
    struct ptr_data *data;

    TypedData_Get_Struct(self, struct ptr_data, &fiddle_ptr_data_type, data);
    data->free = get_freefunc(val, &data->wrap[1]);

    return Qnil;
}