Optional assignment operator. (Discovered after writing this that it had already been thought of, suggested to, and rejected by Swift Evolution)

OptionalAssigment.swift

infix operator ??=
func ??=<T>(lhs: inout T, rhs: T?) {
    guard let rhs = rhs else {
        return
    }
    lhs = rhs
}

// This collapses and obviates redundant-looking use of the nil coalescing operator
// so that given this:

var x: Int = 4
var optionalX: Int? = nil

// instead of doing this:

x = optionalX ?? x

// you can instead do this:

x ??= optionalX