The following program runs out of memory b/c foo is apparently allocated and created every time through the loop:

import std.math, core.memory, std.stdio;

immutable real[] foo = [0,1,2,3,4];

void main() {
    GC.disable;

    foreach(i; 0..1_000_000_000) {
        auto bar = poly(i, foo);
    }
}

Changing the immutable to an enum results in the program still running out of memory.  

Removing all references to immutability fixes the problem.  

Changing the array to a static array fixes the problem.

Initializing the array inside main() fixes the problem.