CODEWITHSUNDEEP
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Voriki
Voriki

Reputation: 1637

Better to add method to pre-defined class or make subclass?

Say you want to add a lengthOfFirstLine method to the predefined File class. Is it a better practice to modify the existing class, or make a new class that extends the File class with your new method?

EDIT -- Specifically, the situation is that a class is lacking one method in particular. I don't want to completely change the class, but rather augment it with that method.

Upvotes: 1

Views: 105

Answers (3)

Chaitanya
Chaitanya

Reputation: 5293

Agree with Luis and Lester. If you are using .Net the extension methods are the way to go for this sort of functionality. But you should try not add LengthOfFirstLine to a base class if you can open all sorts of files such as binary files. You would sub class it to a FileClass and add the method to that.

Remember that the extension methods in .Net are syntactic sugar anyway. You can simulate it in your own language using Static classes and methods. This is what .Net does under the covers anyway.

For example have a static FileHelpers class and have various static helper methods on it. The first parameter for each of these static methods would be the File class. So you could call this using FileHelpers.GetLengthOfFirstLine(myOpenedFile)

Upvotes: 1

Adi Lester
Adi Lester

Reputation: 25201

For .NET languages, there's also the option of using extension methods. This way you don't have to "dirty up" a class by adding helper/utility methods to it, and no inheritance is required as well - you add functionality to a class by simply adding a using statement to your code.

Upvotes: 1

Luis
Luis

Reputation: 1294

It depends if the method is applicable to all elements of the class File. For instance, lengthOfFirstLine doesn't apply to binary files, so probably it doesn't belong in a generic File class, but if your class only represent text files, then it should go there.

Upvotes: 5

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