Extention Methods in Design prttrens in dotnet

Kiran Kumar

1y574Design Patterns & Practices

Implementing Extension Methods in Design pretrains dot net

5 Replies

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Blocked Account1y ago
Accepted answer
Hi Kiran,

Extemsion methos is a language feature but they are often used to implement or support design patterns.

An extension method allows you to "add" new methods to existing types without modifying the original type or creating a new derived type.
```
public static class StringExtensions
{
    public static bool IsNullOrEmpty(this string str)
    {
        return string.IsNullOrEmpty(str);
    }
}
```
In the above code I have just created extension method IsNullOrEmpty, that will retutn bool value true if string is null or empty. It is just one example. You can create as muach as you want.

Thanks
0
Blocked Account1y ago

In the code above, I created two classes. In one class, I used the this keyword in the method parameter, making it an extension method. In the other class, StringExtensionsWithoutThis, I didn’t use this, so it’s just a regular static method.

Now, if you look at the Main method, I declared a string variable. When I type the variable name followed by a dot (.), the extension method appears in the IntelliSense suggestions, but the static method does not. This is because extension methods can be invoked as if they were instance methods on the type they extend.

However, both the extension method and the static method can still be called using the ClassName.MethodName syntax. Since you called the same method in both cases, the output remains the same.
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Kiran Kumar1y ago
Yes, now I can understand the usage of this, but without this mentioned, I didn't get anyway I don't want to get in detail without this as you said it's a rule to have a parameter this while implementing extension method, but my question is how the same logic works without using this and having a static method and invoke it with the class name can you please confirm
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Blocked Account1y ago
If you do not use the this keyword in the first parameter of your method, it is not an extension method-it is just a regular static method. The this keyword in the parameter is what tells the C# compiler to treat the method as an extension method for the specified type.

Key differences:
- With this: You can call the method as if it were a member of the string class (i.e., myString.IsNullOrEmpty()).
- Without this: You must call the method as a static method on the class where it is defined (i.e., StringExtensions.IsNullOrEmpty(myString))
I hope now it's clear to you.
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Kiran Kumar1y ago
HI Dwivedi

Thanks for the information in this pattren do we need to use this keyword I can get the similar result even if dont use this keyeword in function signature can you please confirm

Kiran
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