Closures
Basics of Closures
Understanding closures can be a little tricky for beginners but if you work on it, read it from different sources and understand it correctly, it’s a great tool for clean and high-performance code.
Closures are self-contained code blocks of functionality. Code blocks are given some tasks to do. As you can understand it’s similar to functions. What is the difference? Well, you don’t have to give a name to closure, it can be stored as a variable.
The Syntax
It can be complicated when you see the closure syntax for the first time, to avoid that situation we will compare function and closure syntax. This will help you to understand better.
As you can see above, functions and closures are very similar. There are four types of closures.
- A closure with no parameters and no return value.
2. A closure with parameters and no return value.
3. A closure with no parameters and a return value.
4. A closure with parameters and a return value(like the first example).
Using Closures As Arguments
Many commonly used collection functions and UIKit objects take closures as arguments. Swift has a function named sorted (by: ) which helps you compare two arguments in your Array.
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Now, you can learn how to use a closure as an argument with the example below.
Bonus: There is a shorter way to write closures. Swift is a very smart programing language so it knows that the sorted function is a comparison function that returns a Bool value. So we don’t have to write the return part. Also, you can use $ as a placeholder name. In this case, $0 is our first parameter and $1 is our second parameter to compare. Our previous example is now as short as a line of code.
Swift has some other advanced functions that you can use with closures. I will show you a couple of them today.
Map
You can use the Map function with Arrays. The map function takes a closure parameter that tells it what to do to each object before adding it to the new array. First, I will use “for in loop” for exactly the same example so that you can see how practical to use Map.
It’s time to use Map function with closures.
Filter
The filter function creates a new array associated with the limits you put. For example, from the numbers in an array you have, you can create a new array by taking only numbers less than or greater than 20 with the filter function.
As a result, you can use closures in many ways to solve so many problems. I highly recommend you to search for more articles and examples to learn closures better because you will use them a lot.
