Re: higher-order functions

[bearophile]

Simen kjaeraas:

> They take both, in fact:
> 
> auto cubes = map!((a){ return a*a*a; })(arr);

But that needs to be compile-time constant, so if you have several functions, 
you need to put them inside a typetuple, or duplicate the code. And some idioms 
are just not possible.

You may see it well here regarding the "compose":
http://rosettacode.org/wiki/First-class_functions#D


import std.stdio, std.typetuple, std.functional;
private import std.math;
 
void main() {
    // wrappers needed as not all built-in functions
    // have same signature, eg pure/nothrow
    auto sin  = (real x) { return std.math.sin(x); };
    auto asin = (real x) { return std.math.asin(x); };
    auto cos  = (real x) { return std.math.cos(x); };
    auto acos = (real x) { return std.math.acos(x); };
    auto cube = (real x) { return x ^^ 3; };
    auto cbrt = (real x) { return std.math.cbrt(x); };
 
    alias TypeTuple!(sin,  cos,  cube) dir;
    alias TypeTuple!(asin, acos, cbrt) inv;
 
    foreach (i, f; dir)
        writefln("%6.3f", compose!(f, inv[i])(0.5));
}

Bye,
bearophile