ArrayMinusEqual_Playground.swift

import Swift

@assignment func -=<T, U where T: ArrayType, U: Sequence, T.GeneratorType.Element: Equatable, T.GeneratorType.Element == U.GeneratorType.Element>(inout lhs: T, rhs: U) {
	for removingItem in rhs {
		for (index, item) in enumerate(lhs) {
			if removingItem == item {
				lhs.removeAtIndex(index)
			}
		}
	}
}

var arr1 = [ "one", "two", "three" ]
var arr2 = [ "two", "three" ]
arr1 -= arr2