how do I check if a member of a T has a member ?

[Laeeth Isharc via Digitalmars-d-learn]

On Sunday, 13 September 2015 at 17:34:11 UTC, BBasile wrote:
> On Sunday, 13 September 2015 at 17:24:20 UTC, Laeeth Isharc 
> wrote:
>> On Sunday, 13 September 2015 at 17:09:57 UTC, wobbles wrote:
>>> Use __traits(compiles, date.second)?
>>
>>
>> Thanks.
>>
>> This works:
>>
>> static if (__traits(compiles, { T bar; bar.date.hour;}))
>> 		pragma(msg,"hour");
>> 	else
>> 		pragma(msg,"nohour");
>> 	
>
> can't you use 'hasMember' (either with __traits() or 
> std.traits.hasMember)? It's more idiomatic than checking if 
> it's compilable.

I'll check again in a bit, but I seem to recall hasMember didn't 
work.  I would like to get the type of a member of a type, and I 
think hasMember!(T.bar.date","hour") didn't work for that.  
Possibly it does work and I messed it up somehow, or it doesn't 
work and there is a more elegant way.

Someone ought to write a tutorial showing how to use the good 
stuff we have to solve real problems.  Eg an annotated babysteps 
version of Andrei's allocator talk.  I can't do it as too much on 
my plate.