CODEWITHSUNDEEP
swift
Adrian
Adrian

Reputation: 20058

Closure not called inside object

I am trying to run this simple example using a closure for learning purpose, but doesn't seem to work as I expected:

class Test {
    var callback: ((_ value: Int) -> Void)?

    func perform() {
        callback
    }
}

let t = Test()
t.callback = { _ in
    print("Test")
}

t.perform()

I was expected that "Test" will get printed, but apparently it's not. Can someone point what the issue is ?

Upvotes: 0

Views: 99

Answers (1)

Martin R
Martin R

Reputation: 539685

Compiling the code reveals the error:

error: expression resolves to an unused l-value
        callback
        ^~~~~~~~

callback is just the (optional) closure, not a call to the closure. Apparently the Playground does not complain about the unused expression.

Calling the closure with some argument fixes the problem:

func perform() {
    callback?(5)
}

Upvotes: 1

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