How does the behavior and use of capture lists in closures differ compared to situations without them?

In Swift, closures by default capture variables from the surrounding context by reference, which can lead to strong reference cycles and retain cycles, especially when capturing self.

A capture list is a special syntax in closures that allows you to explicitly specify how variables should be captured: by value (weak, unowned, or copying). This helps control the lifecycle of objects and prevent memory leaks.

Without a capture list, variables are captured automatically and can hold strong references to objects. With a capture list, you can, for example, capture self as weak to avoid retain cycles:

class ViewController {
    var name = "Main"
    func doSomething() {
        let closure = { [weak self] in
            guard let self = self else { return }
            print(self.name)
        }
        closure()
    }
}

Thus, a capture list allows you to:

• Avoid retain cycles
• Capture variables by value or weakly
• Explicitly control capture behavior in closures

Without a capture list, capture occurs automatically and can lead to undesirable consequences.