Lambda Expressions

A lambda expression is just an anonymous method: no access modifier, no name, and no return statement.

Syntax-wise, a lambda expression is exactly like an arrow function in JavaScript.

To see a lambda expression in action, it's useful to store a lambda expression in a delegate:

Func<int, int> square = number => number * number;
Console.WriteLine(square(5)); // prints 25

Note: You may notice that you don't have to provide parameter types or a return type. The compiler infers these types for you.

Another use common use case for lambda expressions is to pass them as arguments to methods. For example, any instance of List has access to the FindAll method. This method accepts a Predicate<T> that must return a bool, which then returns every item in List that returns true.

var books = new BookRepo().GetBooks();
var cheapBooks = books.FindAll(b => b.Price < 10);

Pro tip: By convention, with methods like FindAll, we name the parameter of our lambda expression a single letter because it's clear what we're talking about. That's why the lambda expression is written out as b => b.Price < 10.