Lambda Expressions

In Kotlin, functions are first-class objects. This means they have an equivalent status to the different types of data that we manipulate in a program. Thus it is possible to write higher-order functions that expect to receive another function as an argument, or that return another function to the caller. This is a key aspect of the functional programming paradigm.

These functions that we pass in as arguments are typically quite short. Also, it is common for them to be needed only at one point in the source code. Kotlin therefore allows us to define these functions at the point of use, in a more compact way, as lambda expressions.

The format of a lambda expression (or ‘lambda’, for short) is

{ parameter-list -> body }

This is like a function with no name, and with the parameter list moved inside the braces. An arrow (->) separates the parameter list from the body. No return type is declared, as this will be inferred by the compiler.

After completing this section, you will understand how to create your own lambdas, using a compact syntax. You will also recognize the important role played by lambdas in helping us manipulate collections.