Re: 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{ ... });