An example. This program that uses 2 Predicate instances with the parameterized type of integer. The return value of Predicate types is always bool (true or false).
Part 1 We create a Predicate by assigning to a lambda expression. The predicate has not yet been called.
Part 2 We create a second Predicate, isGreaterEqualFive, and it has an int argument called "x."
Part 3 The program demonstrates how the Invoke method always returns true or false when it is called.
using System;
// Part 1: this Predicate instance returns true if the argument is one.
Predicate<int> isOne = x => x == 1;
// Part 2: this Predicate returns true if the argument is greater than 4.
Predicate<int> isGreaterEqualFive = (int x) => x >= 5;
// Part 3: test the Predicate instances with various parameters.
Console.WriteLine(isOne.Invoke(1));
Console.WriteLine(isOne.Invoke(2));
Console.WriteLine(isGreaterEqualFive.Invoke(3));
Console.WriteLine(isGreaterEqualFive.Invoke(10));True
False
False
True
List. Predicate is often used with the List generic type. You can specify a lambda expression as the argument to certain List methods. The C# compiler then uses type inference.
Step 1 We create a string array of 3 elements. Each string in the array has at least 4 characters.
Step 2 We pass a lambda expression to TrueForAll, which receives a Predicate instance. The return value is a bool.
Result The Predicate returns true if the string has 3 or more chars. This is true for all items in the array, so TrueForAll returns true.
using System;
using System.Collections.Generic;
// Step 1: create list.
var items = new List<string> { "compiler", "interpreter", "file" };
// Step 2: use TrueForAll with a predicate.
if (items.TrueForAll(item => item.Length >= 3))
{
Console.WriteLine("PREDICATE TrueForAll");
}PREDICATE TrueForAll
The right-hand side of a lambda acquires an implicit return value if this is indicated by the context. A Predicate must always have a Boolean return value.
The term "predicate" has wide applicability in computer science. In C#, predicates are specified with lambda expressions where the result value is of type bool.
Dot Net Perls is a collection of pages with code examples, which are updated to stay current. Programming is an art, and it can be learned from examples.
Donate to this site to help offset the costs of running the server. Sites like this will cease to exist if there is no financial support for them.
Sam Allen is passionate about computer languages, and he maintains 100% of the material available on this website. He hopes it makes the world a nicer place.
This page was last updated on May 10, 2023 (rewrite).