Question

Is there any built-in, or library-provided way to map a set of variadic template arguments in D?

For example:

void foo(Args...)(Args args)
{
    bar(fun(args));
}

I want that to expand to:

void foo(Args...)(Args args)
{
    bar(fun(args[0]), fun(args[1]), fun(args[2]), /* ... */);
}

C++11 variadic templates support this. How do you do the same in D?

Answer 1

This is the best I’ve come up with:

auto staticMappedCall(alias call, alias F, T...)(T t)
{
    T a;
    foreach(i, arg; t)
            a[i] = F(arg);
    return call(a);
}

You use it like this:

    staticMappedCall!(bar,t)(1, 2);

Where bar is the function to call and t is the transformation.

void bar(int a, int b) { writeln(a, " ", b); }
int t(int a) { return a*2; }

staticMappedCall!(bar, t)(1, 2);

> test
2 4