On Wednesday, 21 March 2012 at 00:03:28 UTC, James Miller wrote:
template hasAnnotation(alias data, string an) {
enum hasAnnotation = __traits(hasAnnotation, data, an);
}
I'm actually thinking of identifying them by type. Types
are well established in the language - scoping, namespaces,
fields, and so on are all solved.
Querying them is solved too - we can look over a TypeTuple
and use is(typeof()) to get what we want.
(using types as names instead of strings is the idea that
came to me on my ride that prompted this thread - it is the
missing piece in what I wanted here. Strings can conflict,
but types already handle this.)
So you'd just very simply do:
struct MyAttribute { bool activated; }
// @note is just like doing internalTuple ~= MyAttribute(true)
// and MyAttribute is of course just a plain old struct
initializer
@note(MyAttribute(true)) int a;
To check it:
foreach(note; __traits(getNotes, member_a))
static if(is(typeof(note) == MyAttribute) {
// do what you want here, ignore types you don't know
}
Of course, this is in a plain template. No implicit
stuff, no modifying the ast. This data only comes up
when you ask for it, and you ask for it in a plain
old mixin template or something like that - existing
language features.
How far do notes extend?
I'd only put it on declarations (variables,
classes, structs, enums, members, and function
parameters.)
What data can be packed into annotations?
Being able to use custom types is an
important part of my idea here.
