String mixin syntax sugar

[Tove]

On Tuesday, 20 March 2012 at 21:28:25 UTC, Jacob Carlborg wrote:
> On 2012-03-20 19:25, Mantis wrote:
>> Hello,
>>
>> since people discussed a lot about user-defined attributes 
>> recently,
>> I've been thinking about a way to implement it with a string 
>> mixins. The
>> problem with them is their syntax - it's far from what we want 
>> to use in
>> everyday job. I understand, they should be easily 
>> distinguished at use
>> site, but perhaps this may be accomplished in other ways as 
>> well. My
>> idea is to translate this kind of statements:
>>
>> # identifier statement
>>
>> into this:
>>
>> mixin( identifier( q{ statement } ) );
>
>
> I don't like it. I want real user defined attributes.

I think the idea has merit, string mixins together with CTFE 
parsing is the holy grail... because of the current syntax it's 
not really feasible to use on a per-member basis... but it is 
possible to use on a struct/class basis...

mixin(attr(q{struct Foo
{
   @NonSerialized int x;
   @NonSerialized int y;
   int z;
}}));

Please disregard my broken parser(it's just a proof of concept)
However, consider what we could do with the latest CTFE parser 
advances,
coupled with a tighter compiler/library callback interface.
====================================================================

import std.stdio;
import std.array;
import std.string;
import std.algorithm;

string attr(string complex_decl)
{
   string org_struct;
   string ser_struct;

   auto lines = splitLines(complex_decl);

   {
     auto decl = split(stripLeft(lines[0]));

     if(decl[0]=="struct")
     {
       org_struct = decl[0] ~ " " ~ decl[1];
       ser_struct = decl[0] ~ " " ~ decl[1] ~ "_Serializable";
     }
     else
       return complex_decl;
   }

   foreach(line; lines[1..$])
   {
     auto attr = findSplitAfter(stripLeft(line), "@NonSerialized 
");

     if(attr[0]=="@NonSerialized ")
       org_struct ~= attr[1];
     else
     {
       org_struct ~= attr[1];
       ser_struct ~= attr[1];
     }
   }

   return ser_struct ~ "\n" ~ org_struct;
}

mixin(attr(q{struct Foo
{
   @NonSerialized int x;
   @NonSerialized int y;
   int z;
}}));

void main()
{
   auto m = [ __traits(allMembers, Foo) ];
   writeln("Normal members of Foo:", m);

   auto n = [ __traits(allMembers, Foo_Serializable) ];
   writeln("Serializable members of Foo:", n);
}