template parameters

[Charles Hixson]

Thanks.  I going to have to study:

enum supportsCall = isIntegral!(typeof(T.init.%s()));


for awhile to make any sense of that, but it looks like just what I was 
looking for.


On 8/29/21 2:41 PM, Ali Çehreli via Digitalmars-d-learn wrote:
> On 8/29/21 11:32 AM, Charles H. wrote:
>> I've set up a class template (so far untested) thus:
>>
>>      class    AARL (T, ndx = "ndx")
>>              if (isIntegral(T.init.ndx) )
>>
>>      If I'm correct, this should work for ndx an integer variable of 
>> T, but I'd really like T to be able to be anything which can be 
>> stored both in an array and in an associative array.  But I can't 
>> figure out how to specify ndx.  After all, T might be a float, so it 
>> wouldn't have any appropriate attributes.  And I'd also like ndx to 
>> be able to be a function either a member of the class/struct T or a 
>> stand alone function.
>>
>> So how should I set up this template?
>>
>
> I came up with the following:
>
> template supportsCall(T, string func) {
>   import std.format : format;
>   import std.traits : isIntegral;
>
>   enum expr = format!q{
>     enum supportsCall = isIntegral!(typeof(T.init.%s()));
>   }(func);
>
>   mixin (expr);
> }
>
> class AARL (T, string func = "ndx")
> if (supportsCall!(T, func)) {
> }
>
> int ndx(int i) {
>   return 42;
> }
>
> struct S {
>   long ndx() {
>     return 100;
>   }
> }
>
> void main() {
>   auto a = new AARL!int();
>   auto b = new AARL!S();
> }
>
> Ali
>
-- 
Javascript is what you use to allow third part programs you don't know anything about and doing you know not what to run on your computer.