Challenge

[John Colvin via Digitalmars-d]

On Wednesday, 5 October 2016 at 02:15:13 UTC, Jonathan M Davis 
wrote:
> On Wednesday, October 05, 2016 11:20:44 Manu via Digitalmars-d 
> wrote:
>> > While you're at it, might I suggest also adding 
>> > std.traits.isProperty?
>> >
>> >  Something like:
>> > template isProperty(T, string member)
>> > {
>> >
>> >   import std.meta : AliasSeq;
>> >   import std.traits : FunctionTypeOf;
>> >   alias sym = AliasSeq!(__traits(getMember, T, member))[0];
>> >   enum isProperty = !is(typeof(sym) == function) &&
>> >
>> > is(FunctionTypeOf!(typeof(&sym)) == function);
>> > }
>>
>> Why this AliasSeq business? That line is rather an 
>> abomination... why are all these horrible expressions popping 
>> up as recommendations nowadays?
>
> The AliasSeq muck is there because for some reason you can't 
> alias the result of __traits, so doing something like
>
> alias sym = __traits(getMember, T, member);
>
> isn't legal. So, this has nothing to do with a recommendation 
> of best practice and everything to do with an annoying bug.
>
> https://issues.dlang.org/show_bug.cgi?id=7804
>
> It _is_ however recommended to use __traits(getMember, T, 
> member) over manually building it with strings with something 
> like T.stringof ~ "." ~ member, because the string manipulation 
> falls about in corner cases (e.g. it could result in a symbol 
> conflict). It's just that then has the unfortunate side effect 
> of requiring AliasSeq because of the bug.
>
> - Jonathan M Davis

https://dlang.org/phobos/std_meta.html#.Alias   :)