Template parameter-dependent attributes

[Timon Gehr via Digitalmars-d]

On 12/16/2015 06:14 PM, Andrei Alexandrescu wrote:
> So, I wrote this beautiful BigO framework: <400 lines all told, clear
> code, real nice. Then I got this cold shower:
>
> void insertFrontMany(C, R)(C container, R range)
>      @BigO(complexity!(C.insertFront) * linearTime)
> {
>     ...
> }
>
> My hope being of course that for containers with linear insertion time
> at the front I'll get quadratic, etc.

linear and quadratic in what?

> The hitch is:
>
> test.d(377): Error: undefined identifier 'C.insertFront'
>
> So... attributes are currently not allowed to depend on template
> parameters,

Yes, they are.

template bar(T){ @(T.str) auto bar(T t){ } }

struct A{ enum str="str"; }
static assert(__traits(getAttributes,bar!A)[0]=="str");


> ...
>
> Seems to me this is a bug - different instantiations should have
> different attributes etc. Is there any matter of principle making this
> not work?
> ...

No, just a broken lowering in the parser.

auto bar(T)(T t)@(T.str){ }

should be the same as

template bar(T){ auto bar(T t)@(T.str){ } }

It's probably very easy to fix.