CODEWITHSUNDEEP
d
Drathier
Drathier

Reputation: 14539

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.

Upvotes: 3

Views: 103

Answers (2)

BioTronic
BioTronic

Reputation: 2289

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.

Upvotes: 5

Picaud Vincent
Picaud Vincent

Reputation: 10982

It's been a long time since I coded in D, but did you try this as a workaround?

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

Contrary to C++, this is legal in D

Upvotes: 2

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