UDA + Pegged AST Hack

[Daniel N]

Thanks to the wonderful UDA implementation in 2.061, I thought of 
a little hack, which may interest at least someone.

I'm using it for prototyping ctfe ast transformations together 
with: https://github.com/PhilippeSigaud/Pegged

Yes, it was possible to do similar stuff before and 
"examples/dgrammar.d" from Pegged is quite impressive, but not 
bug free.

This UDA-line-hack-way is actually significantly cleaner, because 
when using __LINE__ you are certain that there will be at least 
one [__LINE__] which is not inside a string or comment on the 
attributed line... this allows one to make a very limited 
grammar/parser which doesn't have to know/parse/understand the 
entire file.

I know my proof-of-concept doesn't handle multi-line, but it can 
be added, and doesn't matter for the sake of prototyping AST 
manipulations.

If anyone else have fun UDA hacks, considering that it's a new 
feature, please share.

import std.string;
import std.range;

struct magic
{
   [__LINE__] int var1;
   [__LINE__] int var2;
   [__LINE__] int var3;
}

enum dsrc = import(__FILE__).splitLines(KeepTerminator.yes);

string parse()
{
   string result = "";

   foreach(m; __traits(allMembers, magic))
     result ~= dsrc.drop(__traits(getAttributes, mixin("magic." ~ 
m))[0]-1).takeOne().front;

   // insert pegged parsing / transformations here.

   return result;
}

mixin("struct magic2\n{\n" ~ parse() ~"}");