unbind

static VALUE
method_unbind(VALUE obj)
{
    VALUE method;
    struct METHOD *orig, *data;

    TypedData_Get_Struct(obj, struct METHOD, &method_data_type, orig);
    method = TypedData_Make_Struct(rb_cUnboundMethod, struct METHOD,
                                   &method_data_type, data);
    RB_OBJ_WRITE(method, &data->recv, Qundef);
    RB_OBJ_WRITE(method, &data->klass, orig->klass);
    RB_OBJ_WRITE(method, &data->me, rb_method_entry_clone(orig->me));
    OBJ_INFECT(method, obj);

    return method;
}