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

[John Colvin via Digitalmars-d-learn]

On Monday, 14 September 2015 at 15:04:00 UTC, Laeeth Isharc wrote:
> On Monday, 14 September 2015 at 14:21:12 UTC, John Colvin wrote:
>> On Monday, 14 September 2015 at 14:05:01 UTC, Laeeth Isharc 
>> wrote:
>>> 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:
>>>>> [...]
>>>>
>>>> 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.
>>
>> You mean hasMember!(typeof(T.bar.date), "hour"), right?
>
> Ahh.  Probably that was why (I will check it shortly).  Why do 
> I need to do a typeof?  What kind of thing is T.bar.date before 
> the typeof given that T is a type?

T.bar.date is just a symbol. If you tried to actually access it 
then it would have to be a compile-time construct or be a static 
member/method, but it's perfectly OK to ask what type it has or 
what size it has.

The simple story: hasMember takes a type as its first argument. 
T.bar.date isn't a type, it's a member of a member of a type. To 
find out what type it is, use typeof.