User Defined Attributes

[Daniel Murphy]

"Walter Bright" <newshound2 at digitalmars.com> wrote in message 
news:k7cko9$hes$1 at digitalmars.com...
> On 11/6/2012 6:10 PM, Daniel Murphy wrote:
>> My thoughts exactly.  It reminds me of the horror of C++ exceptions.  I
>> think it would be reasonable to require every annotation is a struct or
>> class.
>
>
> Good analogy. But I'm not sure at this point if that is the right thing to 
> do.

I don't know if it will turn out to be useful either.  But if it's left in 
there, right or wrong, people will use it and it will be impossible to 
remove later.

If two libraries both use string literal annotations for metadata (and they 
will) you can no longer use both on the same declaration at once.  This 
leads back to C/C++'s global namespace.

As an example:
[3] class Blah {}
What on earth is 3?  Why would you want to attach 3 to a class declaration? 
How many different ways are there for libraries to interpret this?

Most importantly, if users still want to experiment with anonymous 
annotations, they still can:
[tuple(3)] class Blah {}
Adding speculative features with no use case in mind is a recipe for 
disaster.

Much like how you can use extern(C) to force global visibility, you can 
still get the less hygienic behaviour, if you explicitly ask for it.

We lose nothing.  If it turns out this was the wrong call, built-in types 
can be restored without breaking a single line of code.