inspect

static VALUE
wmap_inspect(VALUE self)
{
    VALUE str;
    VALUE c = rb_class_name(CLASS_OF(self));
    struct weakmap *w;

    TypedData_Get_Struct(self, struct weakmap, &weakmap_type, w);
    str = rb_sprintf("-<%"PRIsVALUE":%p", c, (void *)self);
    if (w->wmap2obj) {
        st_foreach(w->wmap2obj, wmap_inspect_i, str);
    }
    RSTRING_PTR(str)[0] = '#';
    rb_str_cat2(str, ">");
    return str;
}