• Q. Schroll (33/33) Dec 22 2017 When I wanted something like

Q. Schroll <qs.il.paperinik gmail.com> writes:

When I wanted something like

   static if (enum var = expr)
   { ... }

I did

   static foreach (enum var; { auto x = expr; return x ? [ x ] : [ 
]; }())
   { ... }

The only drawback is, there is no `else`.

You can use the trick even for normal if when the condition is 
not identical to the expression of the declared variable:

   if (auto var = expr) // tests cast(bool)x
   { ... }

Same solution

   foreach (var; { auto x = expr; return cond ? [ x ] : [ ]; }())
   { ... }

Drawback apart from not having else: May allocate if the compiler 
doesn't optimize it. Even then, the code is not  nogc. One would 
use std.range.only for that:

   foreach (var; {
       import std.range : only;
       auto singleton = only(expr);
       if (!cond) singleton.popFront;
       return singleton;
     }())
   { ... }

This can be archived, too, by using std.iteration.filter:

   import std.range : only;
   import std.iteration : filter;
   foreach (var; singleton.only.filter!cond)
   { ... }

Has anyone encountered something similar?

Note that most of the time, you can put the declaration before 
the test. You cannot in mixin templates, where I needed it.