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iOS Swift Basics (retired) Operators Operator Precedence

Posted by Thomas Katalenas
Thomas Katalenas
11,033 Points

a != nil ? a! : b a != nil ? a! : b a != nil ? a! : b a != nil ? a!

a != nil ? a! : b from this webpage at the bottom of the video

https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/BasicOperators.html#//apple_ref/doc/uid/TP40014097-CH6-XID_109

The nil coalescing operator (a ?? b) unwraps an optional a if it contains a value, or returns a default value b if a is nil. The expression a is always of an optional type. The expression b must match the type that is stored inside a.

The nil coalescing operator is shorthand for the code below:

a != nil ? a! : b

The code above uses the ternary conditional operator and forced unwrapping (a!) to access the value wrapped inside a when a is not nil, and to return b otherwise. The nil coalescing operator provides a more elegant way to encapsulate this conditional checking and unwrapping in a concise and readable form.

Note

If the value of a is non-nil, the value of b is not evaluated. This is known as short-circuit evaluation.

here we go so the value of a is non-nil would be a != nil,

what is " a! "mean? and why the colon before b " :b "

a != nil ? a!: b

1 Answer

Jhoan Arango
Jhoan Arango
14,575 Points
Jhoan Arango
Jhoan Arango
14,575 Points

Here is a quick example :

Ternary Operator

var name: String = "Michael"
var lastName: String? = "Arango"

lastName != nil ? lastName! : name // Unwraps lastName since is not nil

var name: String = "Michael"
var lastName: String? =  nil

lastName != nil ? lastName! : name // returns "name" since "lastName" is nil.

Nil Coalescing Operator.

// This does the same as the ternary operator but in a more elegant way.

var name: String = "Michael"
var lastName: String? = "Arango"

lastName ?? name // Unwraps lastName since is not nil

var name: String = "Michael"
var lastName: String? = nil

lastName ?? name // returns "name" since "lastName" is nil

Good luck