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.

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

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...

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.

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...

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...

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. :)

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