Is std.variant.visit not @nogc?

[Paul Backus]

On Monday, 9 April 2018 at 07:07:58 UTC, Chris Katko wrote:
> On Monday, 9 April 2018 at 07:02:50 UTC, Hasen Judy wrote:
>> IMO, this is one more reason why sum-types should be built 
>> into the language compiler, instead of being implemented in 
>> user-space.
>
> +1. Any time you have to "create" a fundamental feature in a 
> language... from inside the language itself... you're going to 
> have confusing error messages, and a huge uphill battle.

I agree in general, but in this case it's actually completely 
doable. In fact, I've done it myself: check out 'sumtype' on 
code.dlang.org. You can replace 'Algebraic' with 'SumType' and 
'visit' with 'match' in helxi's example, and everything Just 
Works™:

import sumtype;

import core.stdc.stdio;

SumType!(T, string) fib_nth(T)(T n)
{
     return n % 15
                 ? n % 5
                     ? n % 3
                         ? SumType!(T, string)(n)
                         : SumType!(T, string)("Fizz")
                     : SumType!(T, string)("Buzz")
                 : SumType!(T, string)("Fizzbuzz");
}

void main() @nogc
{
     foreach (i; 1 .. 101)
     {
         fib_nth(i).match!(
             (string s) => printf("%s\n", s.ptr),
             (int n) => printf("%i\n", n)
         );
     }
}