Composition Inheritance

Question

The advantages of using composition over inheritance are well known;

When is the opposite preferable?

In practice, I see the advantage of forcing the base constructor, but I would like to know the opinions of other people about other cases / domains.

Answer 1

The only advantage of inheritance over the composition that I can think of is that it can potentially save you from a lot of delegation of the boiler plate.

If you really have an is-a relationship and you just want to use all the methods from the base class in your subclass, then inheritance gives you all these methods for free.

Answer 2

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Answer 3

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Answer 4

One of the special cases when I find inheritance is the best solution when I use a class created at runtime that needs additional methods. For example (in C #):

public abstract class Rule{
    /* properties here */
    public Authorization Authorization { get; set; }
    public abstract bool IsValid(dynamic request, User currentUser);
}

Generated Template:

public class Generated_1Rule : Rule{
    public override bool IsValid(dynamic request, User currentUser){
        // the user script is here
    }
}

Example user script:

return Authorization.IsAuthorized("Module_ID_001", currentUser);

The advantage is that you can add functionality to the generated “compiled” script, and it is less broken than it inherits from the interface / composition because it is compiled.