Visual Basic 2012 Programmer's Reference

LAMBDA FUNCTIONS

Lambda functions are functions that are defined within the flow of the program’s code. Often they are defined, used, and forgotten in a single statement without ever being given a name.

To define a lambda function for later use, start with the Function keyword. Add the function’s name and any parameters that it requires, followed by a single statement that evaluates to the value that the function should return.

Next include either (1) a single statement that evaluates to the value that the function should return, or (2) a function body that ends with an End Function statement.

The following code fragment shows examples of both of these styles:

Dim square_it = Function(n As Integer) n * n
Dim factorial = Function(n As Integer) As Integer
                    Dim result As Integer = 1
                    For i As Integer = 2 To n
                        result *= i
                    Next i
                    Return result
                End Function
 
Debug.WriteLine(square_it(5))
Debug.WriteLine(factorial(5))

The code first creates a lambda function named square_it that takes parameter n and returns n * n. It then creates a multiline lambda function named factorial that calculates and returns a number’s factorial. The code finishes by calling both functions and displaying their results.

Example program LambdaFunction, which is available for download on the book’s website, contains the following code fragment:

' Define a lambda function that adds two integers. Dim plus = Function(i1 As Integer, i2 As Integer) i1 + i2 ' Get A and B. Dim A As Integer = Integer.Parse(txtA.Text) Dim ...