gistfile1.d

import std.traits;

struct Signed {}
struct Unsigned {}

struct Wrapper(V, T) {
    private V value;
    private T tag;
    alias value this;

    int opEquals(Wrapper o) const {
        return o.value == value;
    }
}

auto wrap(V)(V v) if (isSigned!V) {
    return Wrapper!(V, Signed)(v);
}

auto wrap(V)(V v) if (isUnsigned!V) {
    return Wrapper!(V, Unsigned)(v);
}

void main() {
    assert(wrap(42) == wrap(42));
    assert(wrap(42) == wrap(42u)); // compile error
}