UDA + Pegged AST Hack

[Philippe Sigaud]

On Wed, Nov 28, 2012 at 10:40 PM, Daniel N <ufo at orbiting.us> 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<https://github.com/PhilippeSigaud/Pegged>


Aha!


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

No kidding :)
I've a few contributors who're helping me stabilize / make the engine
better. We will tackle the D grammar afterwards. It does make a good
testing ground for when I want to push the CTFE throttle.



> 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 don't understand what you're trying to do. Could you please explain it a
bit more? UDA's a quite new and I'd be very interested in their interaction
with compile-time code manipulation.



> 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;
>

What I don't get is how the [__LINE__] part in magic contains significant
info.
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