• Andrea Fontana (7/7) Mar 10 2016 I used to think that classes can't be used with CTFE.
• Adam D. Ruppe (15/17) Mar 10 2016 Classes have worked normally with CTFE for several years now. You
• Andrea Fontana (6/25) Mar 10 2016 Yes but in one case it will print only that message, if instanced

Andrea Fontana <nospam example.com> writes:

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

Adam D. Ruppe <destructionator gmail.com> writes:

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.

Andrea Fontana <nospam example.com> writes:

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 :)