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How do you declare an optional closure as a property in Swift?
I am using this code:
var respondToButton:(sender: UIButton) -> Bool
but the compiler complains that the property is not initialized by the end of the initializer. I believe I can solve this issue by declaring the var as an optional, however, I can not find the correct syntax.
How do I declare this closure property as an optional?
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As shown in the above table, there are three types of closures in Swift, namely global functions, nested functions, and closure expressions. They differ in several aspects, including their use scopes, their names, and whether they capture values, which will be discussed more in a later section.
In Swift, a closure is a special type of function without the function name. For example, { print("Hello World") } Here, we have created a closure that prints Hello World . Before you learn about closures, make sure to know about Swift Functions.
Closures can capture and store references to any constants and variables from the context in which they're defined. This is known as closing over those constants and variables. Swift handles all of the memory management of capturing for you.
A trailing closure is written after the function call's parentheses, even though it is still an argument to the function. When you use the trailing closure syntax, you don't write the argument label for the closure as part of the function call.
I believe you just need to wrap the closure type in parenthesis, like so:
var respondToButton:((sender: UIButton) -> Bool)? Alternatively if this is a closure type you're going to use often you can create a typealias to make it more readable:
typealias buttonResponder = (sender: UIButton) -> Bool then in your class:
var respondToButton:buttonResponder? If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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