Search code examples
d

Static if expression in D?

How can I simulate a static if expression (not statement) in D?

auto foo = (({ static if (cond) { return altA; } else { return altB; })());

This works, but creates a delegate and ldc errors out if you nest delegates. I'm sure it can be done as an expr with some template magic, I'm just not good enough at it yet.

Solution

  • Since static if doesn't create a new scope, you can just do this:

    static if (cond)
    auto foo = altA;
else
    auto foo = altB;

// Use foo here as normal
foo.fun();

    If you really want it to be an expression, you can do this:

    template ifThen(bool b, alias a, alias b) {
    static if (b)
        alias ifThen = a;
    else
        alias ifThen = b;
}

auto foo = ifThen!(cond, altA, altB);

    There are some limitations of alias parameters that may make this solution suboptimal, so it may or may not work for you.