• Klb (39/39) Jul 16 2014 Hello, I'd like to know if it's possible, using CTFE, mixin etc
• bearophile (5/7) Jul 16 2014 I remember Andrei planned to add this small thingie to Phobos,
• Adam D. Ruppe (7/7) Jul 16 2014 Not a direct answer, but the way I'd do this is to just use
• H. S. Teoh via Digitalmars-d-learn (6/16) Jul 16 2014 +1, simple answer to simple question, and `alias this` totally rawks.
• Adam D. Ruppe (4/7) Jul 16 2014 The problem there is names is a regular runtime variable and
• Klb (6/13) Jul 16 2014 Unfortunately I can't encapsulate and alias. Behind the question
• Rene Zwanenburg (4/20) Jul 16 2014 If I understand you correctly, 'wrap' may be what you're looking
• Klb (2/9) Jul 16 2014 Nice ! It works. :)

"Klb" <Klb somewhere.ut> writes:

Hello, I'd like to know if it's possible, using CTFE, mixin etc 
to convert a POD struct to a class at compile time.

I've reached the step where the string to mix-in is generated but 
I cant mix it:

-------------------------------------------------------------
import std.stdio;
import std.traits, std.typetuple;

static private template genClassFromStruct(S) if (is(S == struct) 
&(__traits(isPOD, S)))
{
     auto values = S.init.tupleof;
     auto types = typeid(typeof(values));
     auto names = __traits(allMembers, S);

     string genClassFromStruct()
     {
         string members;
         foreach(int i,t; RepresentationTypeTuple!S)
         {
             members ~= t.stringof ~ " " ~ names[i] ~ ";\r";
         }

         return
             "class c" ~ S.stringof ~
             "{" ~ ";\r"~
                 members ~
             "}";
     }
}

struct foo{ int a; float b;}
//mixin( genClassFromStruct!foo );

void main(string args[])
{
     foo Foo;
     //auto c = new cfoo;

     writeln( genClassFromStruct!foo );
}
-------------------------------------------------------------

The problem appends when un-commenting the mixin:

Error: static variable _names_field_0 cannot be read at compile 
time.

"bearophile" <bearophileHUGS lycos.com> writes:

Klb:

 Hello, I'd like to know if it's possible, using CTFE, mixin etc 
 to convert a POD struct to a class at compile time.

I remember Andrei planned to add this small thingie to Phobos, 
but it's still missing.

Bye,
bearophile

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

Not a direct answer, but the way I'd do this is to just use 
composition:

class Foo {
    YourStruct _this;
    alias _this this;
}


boom, it'd work pretty well just like that...

"H. S. Teoh via Digitalmars-d-learn" <digitalmars-d-learn puremagic.com> writes:

On Wed, Jul 16, 2014 at 06:07:32PM +0000, Adam D. Ruppe via Digitalmars-d-learn
wrote:
 Not a direct answer, but the way I'd do this is to just use
 composition:
 
 class Foo {
    YourStruct _this;
    alias _this this;
 }
 
 
 boom, it'd work pretty well just like that...

+1, simple answer to simple question, and `alias this` totally rawks.
:-)


T

-- 
Famous last words: I *think* this will work...

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

On Wednesday, 16 July 2014 at 17:43:03 UTC, Klb wrote:

     auto names = __traits(allMembers, S);

 Error: static variable _names_field_0 cannot be read at compile 
 time.

The problem there is names is a regular runtime variable and 
mixins need to use compile time stuff. If you make that enum 
instead of auto, it'll probably work.

"Klb" <Klb somewhere.ut> writes:

On Wednesday, 16 July 2014 at 18:09:10 UTC, Adam D. Ruppe wrote:
 On Wednesday, 16 July 2014 at 17:43:03 UTC, Klb wrote:

    auto names = __traits(allMembers, S);

 Error: static variable _names_field_0 cannot be read at 
 compile time.

 The problem there is names is a regular runtime variable and 
 mixins need to use compile time stuff. If you make that enum 
 instead of auto, it'll probably work.

Unfortunately I can't encapsulate and alias. Behind the question 
stands another idea: I do something with an interface 
implementer, as the "something" is not compat. with structs the 
idea was to generate a class as a string, with the interface and 
its default method...

"Rene Zwanenburg" <renezwanenburg gmail.com> writes:

On Wednesday, 16 July 2014 at 18:27:31 UTC, Klb wrote:
 On Wednesday, 16 July 2014 at 18:09:10 UTC, Adam D. Ruppe wrote:
 On Wednesday, 16 July 2014 at 17:43:03 UTC, Klb wrote:

   auto names = __traits(allMembers, S);

 Error: static variable _names_field_0 cannot be read at 
 compile time.

 The problem there is names is a regular runtime variable and 
 mixins need to use compile time stuff. If you make that enum 
 instead of auto, it'll probably work.

 Unfortunately I can't encapsulate and alias. Behind the 
 question stands another idea: I do something with an interface 
 implementer, as the "something" is not compat. with structs the 
 idea was to generate a class as a string, with the interface 
 and its default method...

If I understand you correctly, 'wrap' may be what you're looking 
for:

http://dlang.org/library/std/typecons/wrap.html

"Klb" <Klb somewhere.ut> writes:

On Wednesday, 16 July 2014 at 18:09:10 UTC, Adam D. Ruppe wrote:
 On Wednesday, 16 July 2014 at 17:43:03 UTC, Klb wrote:

    auto names = __traits(allMembers, S);

 Error: static variable _names_field_0 cannot be read at 
 compile time.

 The problem there is names is a regular runtime variable and 
 mixins need to use compile time stuff. If you make that enum 
 instead of auto, it'll probably work.

Nice ! It works. :)