UDA + Pegged AST Hack

[deadalnix]

On Wednesday, 28 November 2012 at 21:40:35 UTC, Daniel N wrote:
> 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() ~"}");

Here we go, annotation with strings. The feature is not even out 
that its quirks already shows up.

You take the least resistance path, and this is comprehensible, 
but anotationg with a string is known to be a bad idea. It have 
been mentionned in UDA and what you did here is the perfect 
example : when the least resistance path is something plain 
wrong, people will do it anyway.

Can someone remember me why this ended up in master ? This 
feature is clearly not ready.