How do I check whether an aggregate member function (call for a specific argument) is @nogc or not?

I want to check whether

    Allocator.allocate(1)

(for a any Allocator) is @nogc or not?

Is

https://dlang.org/phobos/std_traits.html#hasFunctionAttributes

the way to do it?

On Thursday, 11 January 2018 at 12:24:36 UTC, Nordlöw wrote:
> How do I check whether an aggregate member function (call for a specific argument) is @nogc or not?
>
> I want to check whether
>
>     Allocator.allocate(1)
>
> (for a any Allocator) is @nogc or not?
>
> Is
>
> https://dlang.org/phobos/std_traits.html#hasFunctionAttributes
>
> the way to do it?

Is this an ok implementation:

enum bool isNogc(alias fun) = (isCallable!fun &&
                               (functionAttributes!fun &
                                FunctionAttribute.nogc));

@safe pure nothrow @nogc unittest
{
    static int foo(int x) @nogc pure nothrow;
    static int goo(int x) pure nothrow;
    static assert(isNogc!foo);
    static assert(!isNogc!goo);
}

On Thursday, 11 January 2018 at 12:32:54 UTC, Per Nordlöw wrote:
> Is this an ok implementation:
>
> enum bool isNogc(alias fun) = (isCallable!fun &&
>                                (functionAttributes!fun &
>                                 FunctionAttribute.nogc));
>
> @safe pure nothrow @nogc unittest
> {
>     static int foo(int x) @nogc pure nothrow;
>     static int goo(int x) pure nothrow;
>     static assert(isNogc!foo);
>     static assert(!isNogc!goo);
> }

Seems to be working fine. I'd go with this version for perhaps a bit more brevity and clarity:

enum bool isNogc(alias fun) = hasFunctionAttributes!(fun, "@nogc");

Both functionAttributes and hasFunctionAttributes already check that the argument is a callable (which function attributes should "foo" have?), so that's unnecessary.

--
  Simen

On Thursday, 11 January 2018 at 13:18:47 UTC, Simen Kjærås wrote:
> On Thursday, 11 January 2018 at 12:32:54 UTC, Per Nordlöw wrote:
>> Is this an ok implementation:
>>
>> enum bool isNogc(alias fun) = (isCallable!fun &&
>>                                (functionAttributes!fun &
>>                                 FunctionAttribute.nogc));
>>
>> @safe pure nothrow @nogc unittest
>> {
>>     static int foo(int x) @nogc pure nothrow;
>>     static int goo(int x) pure nothrow;
>>     static assert(isNogc!foo);
>>     static assert(!isNogc!goo);
>> }
>
> Seems to be working fine. I'd go with this version for perhaps a bit more brevity and clarity:
>
> enum bool isNogc(alias fun) = hasFunctionAttributes!(fun, "@nogc");
>
> Both functionAttributes and hasFunctionAttributes already check that the argument is a callable (which function attributes should "foo" have?), so that's unnecessary.
>
> --
>   Simen

Author of hasFunctionAttributes here.

FYI: `hasFunctionAttributes` is exactly intended to be used how you do it. functionAttributes is only there for legacy reasons.
And it works nicely with inference too:

https://run.dlang.io/is/9OXZct