Predicate Delegates in C#

Question

Can you explain to me:

• What is a Predicate Delegate?
• Where should we use predicates?
• Any best practices when using predicates?

Answer 1

What is Predicate Delegate?

1) Predicate is a feature that returns true or false.This concept has come in .net 2.0 framework. 2) It is being used with lambda expression (=>). It takes generic type as an argument. 3) It allows a predicate function to be defined and passed as a parameter to another function. 4) It is a special case of a Func, in that it takes only a single parameter and always returns a bool.

In C# namespace:

namespace System
{   
    public delegate bool Predicate(T obj);
}

It is defined in the System namespace.

Where should we use Predicate Delegate?

We should use Predicate Delegate in the following cases:

1) For searching items in a generic collection. e.g.

var employeeDetails = employees.Where(o=>o.employeeId == 1237).FirstOrDefault();

2) Basic example that shortens the code and returns true or false:

Predicate isValueOne = x => x == 1;

now, Call above predicate:

Console.WriteLine(isValueOne.Invoke(1)); // -- returns true.

3) An anonymous method can also be assigned to a Predicate delegate type as below:

Predicate isUpper = delegate(string s) { return s.Equals(s.ToUpper());};
    bool result = isUpper("Hello Chap!!");

Any best practices about predicates?

Use Func, Lambda Expressions and Delegates instead of Predicates.