EducaSwift

Closures are just anonymous functions, they work the same as the functions we already know with the difference that a closure doesn't have a name. This is why we need to assign our closures to a variable.

Creating and using closures

Let's see the difference between a normal function and a closure:

func myFunction(myParameter: String, myOtherParameter: String) -> Int {
    return 12
}

var myClosure: (String, String) -> Int = { myParameter, myOtherPatameter in
    return 12
}

// Execute
let myFunctionResult: Int = myFunction(myParameter: "Hello", myOtherParameter: "World")
let myClosureResult: Int = myClosure(myParameter: "Hello", myOtherParameter: "World")

As you can see, both can execute a block of code, take one or more parameter and return a result. The advantadge of the closure is that it is stored in a variable, meaning that we can use it as a parameter as well.

When to use a closure

Let's see an example where we have a subview that we use to display a custom button. We can add a closure as a property (in this case without any parameters nor a result), so we are able to execute a block of code when the subview executes our closure.

First we create our subview with a closure as a property.

struct MyButton: View {

    let myButtonAction: () -> Void

    var body: some View {
        Button(action: {
            myButtonAction()
        }, label: {
            Text("Button")
                .padding()
                .background(.green)
                .cornerRadius(12)
        })
    }
}

Then we can pass our block of code as a parameter:

struct ContentView: View {

    var body: some View {
        MyButton(myButtonAction: {
            print("Button pressed")
        })
    }
}

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