[]

static VALUE
wmap_aref(VALUE self, VALUE wmap)
{
    st_data_t data;
    VALUE obj;
    struct weakmap *w;
    rb_objspace_t *objspace = &rb_objspace;

    TypedData_Get_Struct(self, struct weakmap, &weakmap_type, w);
    if (!st_lookup(w->wmap2obj, (st_data_t)wmap, &data)) return Qnil;
    obj = (VALUE)data;
    if (!is_id_value(objspace, obj)) return Qnil;
    if (!is_live_object(objspace, obj)) return Qnil;
    return obj;
}