Swift Language Optionals Nil Coalescing Operator
Example
You can use the nil coalescing operator to unwrap a value if it is non-nil, otherwise provide a different value:
func fallbackIfNil(str: String?) -> String {
return str ?? "Fallback String"
}
print(fallbackIfNil("Hi")) // Prints "Hi"
print(fallbackIfNil(nil)) // Prints "Fallback String"
This operator is able to short-circuit, meaning that if the left operand is non-nil, the right operand will not be evaluated:
func someExpensiveComputation() -> String { ... }
var foo : String? = "a string"
let str = foo ?? someExpensiveComputation()
In this example, as foo is non-nil, someExpensiveComputation() will not be called.
You can also chain multiple nil coalescing statements together:
var foo : String?
var bar : String?
let baz = foo ?? bar ?? "fallback string"
In this example baz will be assigned the unwrapped value of foo if it is non-nil, otherwise it will be assigned the unwrapped value of bar if it is non-nil, otherwise it will be assigned the fallback value.
