Introduction to Generic Methods in C#

When we create a method, class or interface, we usually specify the type of the parameter and its return type.

For Example.

Invoke the above function using

This will display 10 in the message box.

Now pass the string to the showValue function as shown below and you will get the compiler error “Invalid arguments” . That is because showValue function expects an integer and not a string;

To solve the problem what we do is write another overloaded function showValue which takes the string as input as shown below.

And invoke the above using the code

Now both will work fine.

Generic Methods in C#

Using Generics

In the above example, We have duplicated the code MessageBox.Show(val.ToString()) in both the functions. This works correctly, but it is not efficient.  If we want to extend the function to handle double data type, then we need to write one more overloaded function repeating the code again.

The solution is to write the code once, which will handle all the types.  And that is where generics come into the picture.

For Example, the above code written in a generic way

And invoke the function using

Defining the Generic Method

Using Generics in C#
Using Generics in C# Using Generics in C#

What is  <T>

<T> is just a placeholder for the data type.  It is more like a blueprint for the type.  T is substituted by the actual type at the runtime.

Instead of <T> you can use <X> and is perfectly valid

Multiple Parameters

Generic methods can have multiple parameters.

Parameters can be of different types. In the example below first parameter, val1 is of a generic type, while second parameter val2 is of type int.

You can have two generic type parameters of the different type as shown below.

Invoked as

Constraints on Parameters

We can specify the restrictions on the types of parameters using the where clause.  A compile-time error is generated when you call your generic method with the wrong types

For Example

Where T:struct

The Value type like int, float, struct etc. must be used as the parameter

and if invoked as

where T : class

Here reference type like string, class, arryays etc. must be used as the parameter. Example :

The Constraints for multiple generic types is as follows

Returning a Generic type From a method

We can specify the return type from a generic method as follows

Generic Classes

Like methods, classes can be made to act on generic types.  The concept is very much similar to the method.  In the example below,  we modified the code GenshowValue and moved it into the class.

And  invoked as

Generic Interfaces and delegates

The Interface and delegates can be made to use generic types similar to the class.

Advantageous of Using C# Generics

  • Allows you to write code which has a similar logic but can be applied to various data types. This enables you to reuse the code
  • Allows you to write type-safe code as  C# Generics are checked at the compile- time. If you use objects instead of generics, then casting to the correct type needs to be done at runtime.
  • Using objects instead of Generics also has the problem of boxing/unboxing of value types or casting in case of reference types.


C# Generic programming allows us the create highly reusable code. Code that can be reused in many different places and situations.  Generics allow us to create methods, classes, interfaces, and delegates work with multiple types while still being type safe.

Further Reading

Introduction to Generics

Source Code

Source Code

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