TL;DR: Favor composition over inheritance

Problems

• Coupling

• Subclassification Reuse

• Bad cohesion

• Fragile base classes

• Method overriding

• Liskov Substitution

Solutions

1. Break classes and compose them.

Context

Old papers recommended using classes as a specialization for code reuse.

We learnt that composition is a more efficient and extensible way to share behavior.

Sample Code

Wrong

classdef Animalia

end

classdef Chordata < Animalia 

end

classdef Mammalia < Chordata 

end

classdef Perissodactyla < Mammalia 

end

classdef Equidae < Perissodactyla  

end

classdef Equus < Equidae 
//Equus behaviour
end

classdef EFerus < Equus
//EFerus behaviour
end

classdef EFCaballus < EFerus
//EFCaballus behaviour    
end

Right

classdef Horse       
    methods        
      // Horse behavior       
    end    
end

Detection

[X] Automatic

Many linters report Depth of inheritance tree (DIT).

Tags

• Hierarchies

Conclusion

Look after your hierarchies and break them often.

Relations

More Info

• Coupling: The one and only problem

• Wikipedia

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Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification.

Bertrand Meyer

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This article is part of the CodeSmell Series.