Action, Func and Predicate Delegate in C#

Sunday 5 April 2015

Action, Func and Predicate Delegate in C#

Action, Func and Predicate Delegate in C#

Delegate is a very powerful feature available in the .NET Framework. In this article, we will explore delegate & its new features which are being introduced in the framework. I will be using Visual Studio 2013 for coding sample code, assuming that you do have basic knowledge of .NET C# code.
I will be explaining the following flavors in these articles:

Action

Ø Action is a delegate (pointer) to a method, that takes zero, one or more input parameters, but does not return anything.

Ø When you want a delegate for a function that may or may not take parameters and does not return a value.

Ø Action is more commonly used for things like List<T>.ForEach: execute the given action for each item in the list..

Ø I use these often for anonymous event handlers:

Ø Example

                    button1.Click += (sender, e) => {/* Do Some Work */}

Func

Func is a delegate (pointer) to a method, that takes zero, one or more input parameters, and returns a value (or reference).
When you want a delegate for a function that may or may not take parameters and returns a value.
The most common example would be Select from LINQ:
Example

                    var result = someCollection.Select( x => new { x.Name, x.Address });

Predicate is a special kind of Func often used for comparisons.

Predicate is a delegate that takes generic parameters and returns bool
When you want a specialized version of a Func that takes evaluates a value against a set of criteria and returns a boolean result (true for a match, false otherwise).
Though widely used with Linq, Action and Func are concepts logically independent of Linq. C++ already contained the basic concept in form of typed function pointers.
Predicate<T> is a delegate that takes a T and returns a bool.
It's completely equivalent to Func<T, bool>.
Predicate is just a special cased Func<T, bool> really, introduced before all of the Func and most of the Action delegates came along
Predicate is mostly used in List<T> for methods like FindAll and RemoveAll.