Think of closures as a piece of code or functionality to pass around in your code. Closures in Swift are very similar to blocks in C and Objective-C. Closures in Swift are the first class type and it is allowed to be returned or passed as a parameter. And as we will see, functions are just special instances of closures. The general formula for closures is like this:

{ (params) -> returnType in
    
    //statements
}

As you can see, we opened curly braces, and then we added the necessary parameters followed by the return type and the in keyword. Knowing this formula will help you a lot in using closures, and you will not feel any frustration using it.

This is an example of using closures in sorting the collection of data:

var nums = [10, 3, 20, 40, 1, 5, 11]
sorted(nums, { (number1, number2) -> Bool in
    return number1 > number2
})
//[40, 20, 11, 10, 5, 3, 1]

Here, the closure is used to identify the comparison result of any two numbers. As we saw, the closure takes two parameters and returns a Boolean, that is the result of the comparison.