Simplifying Conditional Logic

本文同步于个人部落格: Simplifying Conditional Logic

This article references the chapter 10 ” Simplifying Conditional Logic ” of Refactoring: Improving the Design of Existing Code (2nd Edition). Author had highlighted many important refactorings in this chapter.

I use .NET C# to practice with these refactorings and upload to Github.

(Photo from Pixabay: https://pixabay.com/illustrations/direction-path-decision-goal-2320124/)

Decompose Conditional

Tips

If the condition is complex, extract the condition and its branches as functions.

Examples:

A simple example

Github

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Consolidate Conditional Expression

Tips

Some conditions can be reduced into an “Ands” or “Ors” expression. Then this “Ands” or “Ors” expression can be extracted as a function.Sequences combine with Or, nested if statements combine with And.If the conditions have side-effect, use Separate Query from Modifier to process it.

Examples:

An Ors exampleAn Ands example

Github

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Replace Nested Conditional with Guard Clauses

Tips

If a condition is not normal, check it and return if it’s true. This check is a Guard ClauseGuard Clause means that it is not the core logic of the function But if it happens, it does the necessary cleaning job to exit the function.Choose the outermost condition and replace it by Guard Clause. If some Guard Clauses have the same result, use Consolidate Conditional Expression.

Examples:

An simple exampleReversing the Conditions example

Github

Replace Conditional with Polymorphism

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Tips

If a condition is complex, split it by using polymorphism and make its logic clearFor a variation condition, we put the basic logic into a superclass, and put the variation logic into derived class.Don’t abuse using polymorphism when the condition is simple.If the current class has no polymorphism, we create a factory function to return its object instance. Then we put every condition logic into derived class.

Examples:

An simple exampleUsing Polymorphism for Variation

Github

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Introduce Special Case

Tips

If clients always check a structure’s value, we separate this check into a special-case.NullObject is a common pattern for null value.Add the special-case check property to the target structure. Use Combine Functions into Class or Combine Functions into Transform to move the special-case logic into a new class. Then the previous special-case check property will return it when check triggers.

Examples:

A Class exampleAn Object Literal exampleA Transform example

Github

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Introduce Assertion

Tips

Assertion definitely marks the assumption(expression). Assertion avoid programmer’s error.Don’t abuse assertion. We only use it when the expression must be true.

Examples:

// before refactoringpublic void SaveMoneyIntoAccount(decimal money){     acount += money;}// after refactoringpublic void SaveMoneyIntoAccount(decimal money){     Debug.Assert(money > 0);     acount += money;}

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Conclusion

This chapter introduces me how to simplify conditional logic. I had ever written complex conditional branches and they were very ugly long…… I had no idea to reafactor them until I read this chapter. If you want to learn detailed motivation and mechanics, study the chapter 10 ” Simplifying Conditional Logic ” of Refactoring: Improving the Design of Existing Code (2nd Edition). and it improves our programmer’s ability.