Partial application of compile time args type deduction

[QAston via Digitalmars-d-learn]

On Wednesday, 20 January 2016 at 00:12:16 UTC, Ali Çehreli wrote:
> On 01/19/2016 03:37 PM, QAston wrote:
>> Hi,
>>
>> I have the following code:
>>
>> auto appendMapped(alias f, R, T)(R r, T elem) {
>>      r ~= f(elem);
>>      return r;
>> }
>>
>> int minus(int i) {
>>      return -i;
>> }
>>
>> unittest {
>>      int[] ar;
>>          // here I do partial application of minus function
>>      alias appendMinus(S,T) = appendMapped!(minus, S, T);
>>      assert (appendMinus!(int[], int)(ar, 10) == [-10]); // 
>> compiles
>>      assert (appendMinus(ar, 10) == [-10]); // doesn't compile
>> }
>>
>> Which gives me following error:
>> Error: template transduced.__unittestL111_2.appendMinus cannot 
>> deduce
>> function from argument types !()(int[], int), candidates are:
>> transduced.__unittestL111_2.appendMinus(S, T)
>>
>> Is there a way to do partial template arg application which 
>> does
>> template type deduction correctly?
>
> I don't know whether it's possible with 'alias' but the 
> following trivial wrapper works:
>
>     auto appendMinus(S,T)(S s, T t) {
>         return appendMapped!minus(s, t);
>     }
>
> Ali

I think I've reduced my case too much: the wrapper needs to be 
generic so that I can do something like this (basically a closure 
but compile time)

void wrapper(minus) {
     alias appendMinus(S,T) = appendMapped!(minus, S, T);
     assert (appendMinus(ar, 10) == [-10]);
}

Anyway, thanks for help Ali, love your book:)