Optional chaining is one of the great, useful features of Swift. It can be used
“for querying and calling properties, methods, and subscripts on an optional
that might currently be nil,” to quote Apple's "The Swift Programming
Language.” However, often it is necessary to call a function, subscript, or
initializer conditionally based on if one or more parameters are nil. The
proposed solution is to allow a question mark (?) to be placed after an
optional value wished to be used as a parameter. Then, the function,
initializer, or subscript will be called if and only if the parameter's value
is not nil. If it has a return type, it will return an optional, which will be
nil if the parameter is nil.
Old way (with seemingly unnecessary if statement considering the flexibility
provided by optional chaining):
var arr = ["apples", "oranges", "pears", "bananas"]
let index: Int? = 2
var removedElement: String?
if let index = index {
removedElement = arr.removeAtIndex(index) //sets removedElement
to "pears"
}
Using this proposal:
var arr = ["apples", "oranges", "pears", "bananas"]
let index: Int? = 2
var removedElement: String?
removedElement = arr.removeAtIndex(index?) //sets removedElement to
“pears"
Another similar example:
Old way:
var arr = ["apples", "oranges", "pears", "bananas"]
let index: Int? = nil
var removedElement: String?
if let index = index {
removedElement = arr.removeAtIndex(index) //never called
}
Using this proposal:
var arr = ["apples", "oranges", "pears", "bananas"]
let index: Int? = nil
var removedElement: String?
removedElement = arr.removeAtIndex(index?) //removeAtIndex is never
called, and removedElement is set to nil
What does everyone think of this proposal? It is additive so it will not break
any existing code, and in the future it will provide conciseness and clarity
since the syntax is similar to the existing optional chaining syntax.
View the full proposal on GitHub here:
https://github.com/liam923/swift-evolution/blob/master/proposals/NNNN-extend-optional-chaining-to-function-initializer-and-subscript-parameters.md
<https://github.com/liam923/swift-evolution/blob/master/proposals/NNNN-extend-optional-chaining-to-function-initializer-and-subscript-parameters.md>
Liam_______________________________________________
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