lazy var in ios swift

This article explains the working of lazy var in swift.You must have some knowledge in closures.

Read this article for more info on closures.

While dealing with iOS app development we should be really very much conscious about the amount of memory used by the application. If the app is a complex one, then the memory issues are one of the major challenges for the developer. So, the developer should be really writing an optimised code which consider memory allocation at first place. The developer need to avoid doing expensive work unless it’s really needed. These complex allocations will take more time and it will seriously affect the performance of the application as well.

Swift has a mechanism built right into the language that enables just-in-time calculation of expensive work, and it is called a lazy variable. These variables are created using a function you specify only when that variable is first requested. If it’s never requested, the function is never run, so it does help save processing time.

Apple’s official documentation says:

A lazy stored property is a property whose initial value is not calculated until the first time it is used. You indicate a lazy stored property by writing the lazy modifier before its declaration.

You must always declare a lazy property as a variable (with the var keyword), because its initial value might not be retrieved until after instance initialization completes. Constant properties must always have a value before initialization completes, and therefore cannot be declared as lazy.

To explain this, I will use a basic example: Consider a struct called InterviewCandidate. It has an optional bool value to decide if the candidate is applying for ios or android. Resume description for iOS and android are declared as lazy variables. So , in the following code, the person is an iOS developer and the lazy variable iOSResumeDescription will be initialized when called for printing . androidResumeDescription will be nil.