Identifying associative array types from a template?

[Christopher Wright]

Kirk McDonald wrote:
> Christopher Wright wrote:
>> I want to identify the types that make up an associative array that I 
>> get as a template parameter, something like:
>>
>> template decomposeAA (T) {
>>    static if (is (TT TVal : TVal[TKey])) {
>>       alias Tuple!(TVal, TKey) decomposeAA;
>>    } else {
>>       static assert (false, "not an associative array");
>>    }
>> }
>>
>>
>> Now, if I put conditions on TKey, this works, at least in D2. If I 
>> don't put conditions on TKey, it always static asserts, even if I give 
>> it an associative array.
>>
>> Is this a bug? Is there another way to get the key type and value type?
> 
> Pyd has used this template for about as long as I can remember:
> 
> template isAA(T) {
>     const bool isAA = 
> is(typeof(T.init.values[0])[typeof(T.init.keys[0])] == T);
> }
> 
> Writing an AA decomposing template is easy, given that:
> 
> template decomposeAA(T) {
>     static assert(isAA!(T), "Not an associative array!");
>     alias Tuple!(typeof(T.init.values[0]), typeof(T.init.keys[0])) 
> dcomposeAA;
> }
> 

Thanks, I wound up doing essentially that. I guess I'll avoid attempting 
complex is expressions in the future; I don't understand them very well.