DRY version of `static if(__traits(compiles, expr)) fun(expr)`

[Timon Gehr via Digitalmars-d-learn]

On 15.12.2016 01:38, Basile B. wrote:
> On Wednesday, 14 December 2016 at 22:06:35 UTC, Ali Çehreli wrote:
>> On 12/14/2016 09:25 AM, Basile B. wrote:
>> > On Tuesday, 13 December 2016 at 23:37:59 UTC, Timon Gehr
>> wrote:
>>
>> >> I usually do
>> >>
>> >> enum code = q{expr};
>> >> static if(__traits(compiles,mixin(code)))
>> >>     fun(mixin(code));
>> >
>> > Strangely if i put this in a templated enum that doesn't work.
>> > If instead i use a delegate literal it works.
>> >
>> > enum Compiles(string code) = is(typeof((){mixin(code);}));
>> >
>> > enum Compiles2(string code) = __traits(compiles, mixin(code));
>>
>> When you do that, the code does not match the syntax of
>> __traits(compiles). Putting the code inside a scope works at least in
>> this case:
>>
>> enum Compiles2(string code) = __traits(compiles, mixin('{' ~ code ~
>> '}'));
>>
>> Ali
>
> I see, it makes sense. Anyway the two templates have a common problem
> (protection attributes: data used in the code must be visible to the
> outside), so using them as a shortcut is a false good idea.

Shortcut that works:

enum ifCompiles(string code)=`static if(__traits(compiles,{ `~code~` 
})){ `~code~` }`;

mixin(ifCompiles!q{ ... });