Swift Functional Programming - Second Edition

Closures

Closures are great tools for FP as they are functions without the func keyword and name. Like functions, closures are self-contained blocks of code that provide a specific functionality and can be stored, passed around, and used in the code. Closures capture the constants and variables of the context in which they are defined. Although closures are the equivalent of blocks in Objective-C, they have a simpler syntax in Swift compared to the C and Objective-C block syntax. Nested functions, which we have covered in a previous section, are special cases of closures. Closures are reference types that can be stored as variables, constants, and type aliases. They can be passed to and returned from functions.