Eliminating code duplication for static/nonstatic functions

[Dmitry Olshansky]

19-Sep-2013 21:10, Andrei Alexandrescu пишет:
> Consider a struct that may or may not have state depending on a type
> parameter:

[snip]

> Any ideas for a clean solution? I can't get much further than string
> mixins, which wouldn't be clean :o).

It seems like s/string/template and we are there.

This works for me:

import std.traits;

struct Static{
     static int method(){ return 21; }
}

struct Instance{
     int v; //so that it "hasState"
     int method(){ return 12; }
}

mixin template Methods()
{
     int method() { return 1 + _theT.method(); }
}

struct S(T)
{
   enum hasState = FieldTypeTuple!T.length || isNested!T;
   static if (hasState)
     T _theT;
   else
     alias _theT = T;
   static if (hasState)
         mixin Methods!();
   else{
     static{
         mixin Methods!();
     }
   }
}

void main()
{
     S!Static s1;
     S!Instance s2;
     assert(S!Static.method() == 22);
     assert(s1.method() == 22);
     assert(s2.method() == 13);
     assert(s1.sizeof == 1);
     assert(s2.sizeof == 4);
}

-- 
Dmitry Olshansky