Function tuples

[bearophile]

This comes from a Rosettacode entry:
http://rosettacode.org/wiki/First-class_functions#D

import std.stdio, std.math, std.typetuple, std.functional;

enum static sin  = (in real x) pure nothrow => std.math.sin(x),
            asin = (in real x) pure nothrow => std.math.asin(x),
            cos  = (in real x) pure nothrow => std.math.cos(x),
            acos = (in real x) pure nothrow => std.math.acos(x),
            cube = (in real x) pure nothrow => x ^^ 3,
            cbrt = (in real x) /*pure*/ nothrow => 
std.math.cbrt(x);

void main() {
    alias dir = TypeTuple!(sin,  cos,  cube);
    alias inv = TypeTuple!(asin, acos, cbrt);
    foreach (immutable i, f; dir) {
        writefln("%6.3f %6.3f",
                 compose!(f, inv[i])(0.5),
                 compose!(dir[i], inv[i])(0.5));
    }
}

It prints:

 0.500  0.500
 0.866  0.500
 0.713  0.500

Do you know why there's such difference in the results?

(You can't define a staticZip in D?)

Bye,
bearophile