Attributes on Enum Members: Call for use cases.

[Steven Schveighoffer]

On 11/29/17 4:46 PM, Timon Gehr wrote:
> On 29.11.2017 20:49, Steven Schveighoffer wrote:
>> On 11/29/17 2:01 PM, Timon Gehr wrote:
>>
>> OK, now I get what you are saying. In the same vein, I tested applying 
>> attributes to functions themselves:
>>
>> @("a") int fun() { return 0; }
>> pragma(msg, typeof(&fun)); // int function()
>>
>> @("b") int gun() { return 1; }
>> pragma(msg, typeof(&gun)); // int function()
>>
>> void main()
>> {
>>    auto f = &fun;
>>    f = &gun; // works
>> }
>>
>> Given that, it seems attributes play no part in the type itself, they 
>> are just metadata in the compiler.
> 
> Well, I think the case of UDAs on parameters is closer to:
> 
> struct S{
>      @("a") int x1;
>      @("b") int x2;
> }
> 
> The attributes on x1 and x2 are indeed part of the type S, even if the 
> attributes on S itself are not.

Right, but unlike functions, you can't make another "overload" of a struct.

> 
> If we go with "UDAs on parameters are not part of the function type", 
> how to you get the UDAs of the parameters of some function?

Looking at std.traits, it looks like we use this mechanism to get 
everything:

int func(int param1)

static if(is(typeof(func) F == __parameters))
{
     static assert(is(typeof(F[0]) == int));
     static assert(__traits(identifier, F[0]) == "param1");
}

This is how vibe.d associates the function-level attributes with the 
name of the parameter.

It wouldn't be a giant leap to make this work with attributes as well.

-Steve