Swift 4 custom argument labels - required? [closed]

问题

func greet (person person: String, on day: String) -> String {
    return "Hello \(person) on \(day)"
}

can be executed as

greet ("John", "23")

Swift 4 - custom argument labels behave as no argument label - "_".

How to make custom labels mandatory for execution?

greet (person: "John", on: "23")

Thanks.

Edit - question is incorrect, as custom labels are mandatory

回答1:

In Swift each function parameter can have both argument label and a parameter name.

argument label: used in function call
parameter name: used inside the function definition

By default, parameters use their parameter name as their argument label.

These are the possible function declarations that can be used in swift:

Case 1: parameter name is same as the argument label

func greet (person: String, day: String) -> String {
    return "Hello \(person) on \(day)"
}

Function Call: greet(person: "John", day: "23")

Case 2: different parameter name and argument label

func greet (person person: String, on day: String) -> String {
    return "Hello \(person) on \(day)"
}

Function Call: greet(person: "John", on: "23")

Case 3: using _ as argument label

func greet (_ person: String, _ day: String) -> String {
    return "Hello \(person) on \(day)"
}

Function Call: greet("John", "23")

For more on how function parameters work, you can refer to: https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Functions.html

Let me know if you still face any issues.

来源：https://stackoverflow.com/questions/49349247/swift-4-custom-argument-labels-required

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swift

function

arguments