The definition of templates in D

[FeepingCreature]

On 03/18/12 11:36, FeepingCreature wrote:
> On 03/18/12 11:29, Derek wrote:
>> On Sun, 18 Mar 2012 19:16:02 +1100, Andrej Mitrovic <andrej.mitrovich at gmail.com> wrote:
>>
>>> On 3/18/12, Derek <ddparnell at bigpond.com> wrote:
>>>> What would be useful is ...
>>>>   bar!(a, b, c); // is equivalent to
>>>>   bar!(int, int, int).bar(a, b, c);
>>>
>>> You mean like this?
>>>
>>> template bar(T...)
>>> {
>>>     void bar() { writeln(T); }
>>> }
>>>
>>> void main()
>>> {
>>>     int a = 1, b = 2, c = 3;
>>>     bar!(a, b, c);
>>> }
>>
>> Almost, but more like this ...
>>
>> template add(X,Y,Z)
>> {
>>    X add(Y a, Z b)
>>    {
>>        return cast(X) (cast(X)a + cast(X)b);
>>    }
>> }
>>
>> void main()
>> {
>>      double s;
>>      int   t;
>>      ulong u;
>>
>>      s = 1.23;
>>      t = 123;
>>      u = 456;
>>
>>     t = add!(u,s);
>>
>>     writefln( "%s %s %s", s,t, u );
>> }
>>
>>
>>
>> This currently errors with ...
>>
>>   "Error: template instance add!(u,s) add!(u,s) does not match template declaration add(X,Y,Z)"
>>
> why would you do that
> 
> what do you want to _do_
> 
> it sounds like you're frantically trying to nail templates into a shape that they really really really aren't meant for
> 
> in any case what is wrong with auto add(T)(T t) { return t[0] + t[1]; }

oh

you may have misunderstood me

a template is a **compile time parameterized namespace**

its parameters are **types** and **constants**, not runtime values

"add" is a "namespace that is instantiated with the types float and"

OOOOOOOOOOOOOOOOOOOOH
I get what you want. :D

template add(T) {
  template add(U...) {
    auto add(U u) {
      T res;
      foreach (value; u) res += value;
      return res;
    }
  }
}

void main()
{
     double s;
     int   t;
     ulong u;

     s = 1.23;
     t = 123;
     u = 456;

     t = add!int(u, s);

    writefln( "%s %s %s", s, t, u );
}