Re: Partial application of compile time args type deduction

[Ali Çehreli via Digitalmars-d-learn]

On 01/19/2016 04:22 PM, QAston wrote:
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:)

Is this it? If so, is it already in std.functional? (I could not find 
it. :) )

auto appendMapped(alias f, R, T)(R r, T elem) {
    r ~= f(elem);
    return r;
}

int minus(int i) {
    return -i;
}

unittest {
    int[] ar;

    template bindFirstParam(alias original, alias func, Args...) {
        auto bindFirstParam(Args...)(Args args) {
            return original!(func, Args)(args);
        }
    }

    alias appendMinus = bindFirstParam!(appendMapped, minus);

    assert (appendMinus!(int[], int)(ar, 10) == [-10]); // compiles
    assert (appendMinus(ar, 10) == [-10]); // doesn't compile
}

void main() {
}

Ali