I used to think that classes can't be used with CTFE.

Instead it appears to work, if they're not directly returned but, for example, they're wrapped inside a struct as on example [1]. Ctor is called *only* at compile time, and instance works fine.

So, I can't understand: why wrapping a class inside a struct make it works?


Ex: http://dpaste.dzfl.pl/5879511dff02

On Thursday, 10 March 2016 at 13:56:18 UTC, Andrea Fontana wrote:
> I used to think that classes can't be used with CTFE.

Classes have worked normally with CTFE for several years now. You don't need to do anything special with them.

> Ex: http://dpaste.dzfl.pl/5879511dff02

This just doesn't do what you think it does:

if (__ctfe) pragma(msg, "compile-time");

That will ALWAYS print the thing because if(__ctfe) is a *run time* branch, and pragma(msg) is a compile time thing. The code gets compiled, even if __ctfe == false, so it will print anyway.

enum forceCTFE(alias expr)=expr;


That's only one way to do CTFE. Notice the error message:

variable p.forceCTFE!(willnot).forceCTFE : Unable to initialize enum with class or pointer to struct. Use static const variable instead.



enums don't work in references, so you do a static variable instead. Static variables are still CTFE'd.

On Thursday, 10 March 2016 at 14:36:18 UTC, Adam D. Ruppe wrote:
> On Thursday, 10 March 2016 at 13:56:18 UTC, Andrea Fontana wrote:
>> I used to think that classes can't be used with CTFE.
>
> Classes have worked normally with CTFE for several years now. You don't need to do anything special with them.
>
>> Ex: http://dpaste.dzfl.pl/5879511dff02
>
> This just doesn't do what you think it does:
>
> if (__ctfe) pragma(msg, "compile-time");
>
> That will ALWAYS print the thing because if(__ctfe) is a *run time* branch, and pragma(msg) is a compile time thing. The code gets compiled, even if __ctfe == false, so it will print anyway.

Yes but in one case it will print only that message, if instanced at runtime it will print the other too. I was just verifing if ctor was called correctly (in a more complex code)

>
> enum forceCTFE(alias expr)=expr;
>
>
> That's only one way to do CTFE.

I just wanted to be sure it is ctfe.

> Notice the error message:
>
> variable p.forceCTFE!(willnot).forceCTFE : Unable to initialize enum with class or pointer to struct. Use static const variable instead.
>
>
>
> enums don't work in references, so you do a static variable instead. Static variables are still CTFE'd.

So problem is actually enum, not ctfe. Nice. Thank you :)