Function.withAttributes

nothrow int answer();
enum model = refract!(answer, "answer");
with (FunctionAttribute) {
    mixin(
        model
        .withName("pureAnswer")
        .withAttributes(model.attributes | pure_)
        .mixture);
    static assert(functionAttributes!pureAnswer & pure_);
    static assert(functionAttributes!pureAnswer & nothrow_);
}