Code Smell 137 - Inheritance Tree Too Deep

Yet another bad code reuse symptom

TL;DR: Favor composition over inheritance

Problems

• Coupling

• Subclassification Reuse

• Bad cohesion

• Fragile base classes

• Method overriding

• Liskov Substitution

Solutions

1. Break clases 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

Code Smell 11 - Subclassification for Code Reuse

Maxi Contieri ・ Oct 30 '20

#oop #codenewbie #tutorial

Code Smell 43 - Concrete Classes Subclassified

Maxi Contieri ・ Dec 5 '20

#oop #codenewbie #tutorial #webdev

Code Smell 58 - Yo-yo Problem

Maxi Contieri ・ Jan 24 '21

#codenewbie #codesmell #tutorial #webdev

Code Smell 37 - Protected Attributes

Maxi Contieri ・ Nov 29 '20

#oop #webdev #tutorial #codenewbie

Code Smell 125 - 'IS-A' Relationship

Maxi Contieri ・ Mar 26 '22

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

Software Engineering Great Quotes

Maxi Contieri ・ Dec 28 '20

#codenewbie #programming #quotes #software

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This article is part of the CodeSmell Series.

How to Find the Stinky parts of your Code

Maxi Contieri ・ May 21 '21

#codenewbie #tutorial #codequality #beginners