Creating variables that call a function of the same name

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Creating variables that call a function of the same name 관련

HACKING WITH SWIFT

What's new in Swift?

Creating variables that call a function of the same name | Changes in Swift 5.4

Creating variables that call a function of the same name

Available from Swift 5.4

From Swift 5.4 onwards it’s possible to create a local variable by calling a function of the same name. That might sound obscure, but it’s actually a problem we hit all the time.

For example, this creates a struct with a color(forRow:) method, which gets called and assigned to a local variable called color:

struct Table {
    let count = 10

    func color(forRow row: Int) -> String {
        if row.isMultiple(of: 2) {
            return "red"
        } else {
            return "black"
        }
    }

    func printRows() {
        for i in 0..<count {
            let color = color(forRow: i)
            print("Row \(i): \(color)")
        }
    }
}

let table = Table()
table.printRows()

That kind of usage is only allowed from Swift 5.4 and later. In earlier versions of Swift, it would create a circular reference because Swift couldn’t distinguish between the local color constant and the color(forRow:) method it was calling – you would have seen the error “Variable used within its own initial value”.

This usually resulted in us either using self.color(forRow: 1989) to make it clear we mean the method call, or just naming the local value something else such as colorForRow.

Fortunately Swift 5.4 resolves this (apple/swift) and allows us to use the more natural naming.

This change also allows us to make local copies of properties and global variables. For example, we can take a copy of a username property that is also called username, like this:

struct User {
    let username = "Taylor"

    func suggestAlternativeUsername() -> String {
        var username = username
        username += String(Int.random(in: 1000...9999))
        return username
    }
}

let user = User()
user.suggestAlternativeUsername()

Because this also applies to global variables, that same code works just fine even without the struct in place:

let username = "Taytay"

func suggestAlternativeUsername() -> String {
    var username = username
    username += String(Int.random(in: 1000...9999))
    return username
}

suggestAlternativeUsername()