TL;DR: Don't read and write the same variable for different purposes

Problems

• Readability

• Hidden problems

Solutions

1. Don't reuse variables

2. Extract Method to isolate scopes

Context

When programming a script it is common to reuse variables.

This leads to confusion and makes debugging harder.

We should narrow the scope as much as possible.

Sample Code

Wrong

// print line total
double total = item.getPrice() * item.getQuantity();
System.out.println("Line total: " + total );

// print amount total 
total = order.getTotal() - order.getDiscount();
System.out.println( "Amount due: " + total );

// variable is reused

Right

function printLineTotal() {
  double total = item.getPrice() * item.getQuantity();
  System.out.println("Line total: " + total );
}

function printAmountTotal() {
  double total = order.getTotal() - order.getDiscount();
  System.out.println( "Amount due: " + total );
}

Detection

[X] Automatic

Linters can use the parse tree to find variable definition and usages.

Tags

• Readability

Conclusion

Avoid reusing variable names. Use more specific and different names.

Relations

More Info

Credits

Photo by Sigmund on Unsplash

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Simplicity before generality, use before reuse.

Kevlin Henney

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This article is part of the CodeSmell Series.