||= operator in Swift

operator.swift

infix operator ||= { associativity left precedence 150 }

public func ||= <T>(lhs: inout T?, rhs: T?) {
    if lhs == nil { lhs = rhs }
}

var a: Int? = nil
a ||= 10
print(a)

var b: Int? = 20
b ||= 10
print(b)