ObjectSpace::WeakMap#[]=

static VALUE
wmap_aset(VALUE self, VALUE key, VALUE val)
{
    struct weakmap *w;
    TypedData_Get_Struct(self, struct weakmap, &weakmap_type, w);

    VALUE pair[2] = { key, val };

    st_update(w->table, (st_data_t)pair, wmap_aset_replace, (st_data_t)pair);

    RB_OBJ_WRITTEN(self, Qundef, key);
    RB_OBJ_WRITTEN(self, Qundef, val);

    return nonspecial_obj_id(val);
}