How to avoid code duplication in static if branches?

[Mantis]

04.03.2012 3:42, Andrej Mitrovic пишет:
> [...code...]
> I want to avoid writing "check()" twice. I only have to statically
> check a field of a member if it's of a certain type (Foo).
>
> One solution would be to use a boolean:
> void test(T)(T t)
> {
>      bool isTrue = true;
>      static if (is(T == Foo))
>          isTrue = t.isTrue;
>
>      if (isTrue)
>          check();
> }
>
> But that kind of defeats the purpose of static if (avoiding runtime
> overhead). Does anyone have a trick up their sleeve for these types of
> situations? :)
>

Alias maybe?

void test(T)( T t ) {

enum TRUE = true;

static if( is(T == Foo) ) {
alias t.isTrue isTrue;
} else {
alias TRUE isTrue;
}

if( isTrue ) {
check();
}

}

This will still insert a redundant check for one of instantiations, but 
compiler should be able to deal with 'if(true)' checks.