static if check for array and AA

[Kirk McDonald]

BCS wrote:
> Kirk McDonald wrote:
> 
>> I'm fairly certain I've seen this come up before, but I can't seem to 
>> rediscover the thread.
>>
>> I'm trying to write a static if condition to check whether a certain 
>> type is an array, and another check for an associative array. The 
>> former proved to be moderately simple:
>>
>> bool isArray(T) () {
>>     static if (is(typeof(T.init[0])[] == T)) {
>>         return true;
>>     } else {
>>         return false;
>>     }
>> }
>>
>> Note that this only checks for dynamic arrays.
>>
>> Associative arrays are harder. The above trick can't quite work as the 
>> type of the key can't be relied upon. It's easy enough to do the check 
>> using RTTI:
>>
>> bool isAA(T) () {
>>     TypeInfo t = typeid(T);
>>     if (cast(TypeInfo_AssociativeArray) t) {
>>         return true;
>>     } else {
>>         return false;
>>     }
>> }
>>
>> But of course that is a runtime check, and this should really be a 
>> compile-time check. (Also, the various subclasses of TypeInfo are 
>> undocumented, so I'm not sure if it's a good idea to rely on them.)
>>
>> Anyone else have some template judo to share?
>>
>> -Kirk McDonald
> 
> 
> 
> template isAA(T)
> {
>     const isAA = is((cast(T)null).keys);
> }
> 
> ???
> 
> or something like that

Now there's an idea... The templates are now:

template isArray(T) {
     const bool isArray = is(typeof(T.init[0])[] == T);
}

template isAA(T) {
     const bool isAA = 
is(typeof(T.init.values[0])[typeof(T.init.keys[0])] == T);
}

I'd forgotten about those .keys and .values properties. :-)

-Kirk McDonald