Testing D arrays for a matching entry

Unfortunately in isn't supported for arrays. Instead, call canFind or search from std.algorithm http://dlang.org/phobos/std_algorithm.html. Here you need presence rather than a position, making canFind the appropriate tool to use here.

import std.algorithm: canFind;

if (items.canFind(36)) { work }

Besides canFind, countUntil is available too and returns the position where the element first appears.

Remember that D's "in" looks through keys in an associative array, rather than through its values :

string[string] entries = [
    "left" : "right"
];

writeln(("left" in entries) != null); // true
writeln(("right" in entries) != null); // false