本文同步於個人部落格: 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

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 example
• An Ands example

Github

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 Clause
• Guard 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 example
• Reversing the Conditions example

Github

Replace Conditional with Polymorphism

Tips

• If a condition is complex, split it by using polymorphism and make its logic clear
• For 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 example
• Using Polymorphism for Variation

Github

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 example
• An Object Literal example
• A Transform example

Github

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 refactoring
public void SaveMoneyIntoAccount(decimal money)
{
     acount += money;
}

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

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.