Variable reuse is something we see in big chunks of code.

TL;DR: Don't reuse variable names. You break readability and refactor chances and gain nothing but laziness.

Problems

• Readability

• Refactor chances

• Missed Optimization

• Mutability

• Garbage Collection Missed Opportunities

Solutions

1. Define, use and dispose variables.

2. Keep your Definition, Usage and Destroy variables short.

Sample Code

Wrong

class Item:
  def __init__(self, name):
    self.name = name
  def taxesCharged(self):
    return 1;
class Money:
  pass 

lastPurchase = Item('Soda');
# Do something with the purchase

taxAmount = lastPurchase.taxesCharged();
# Lots of stuff related to the purchase
# I drink the soda

# I cannot extract method from below without passing
# useless lastPurchase as parameter

# a few hours later..
lastPurchase = Item('Whisky');
# I bough another drink

taxAmount += lastPurchase.taxesCharged();

Right

class Item:
  def __init__(self, name):
    self.name = name
  def taxesCharged(self):
    return 1;
class Money:
  pass 

def buySupper():
  supperPurchase = Item('Soda');
  # Do something with the purchase

  # Lots of stuff related to the purchase
  # I drink the soda
  return supperPurchase;

def buyDrinks():
  # I could extract method! 

  # a few hours later..
  drinksPurchase = Item('Whisky');
  # I bough another drink

  return drinksPurchase;

taxAmount = buySupper().taxesCharged() + buyDrinks().taxesCharged();

Detection

Many linters can warn us from reusing variables

Tags

• Readability

Conclusion

Reusing variables is a non-contextual copy and paste hint.

Relations

More Info

• The Evil power of Mutants

• Stack Exchange

• Wikiversity

Credits

Photo by Robby McCullough on Unsplash

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Either way you look at it (DRY or laziness), the idea is the same: make your program flexible. When change comes (and it always does), you'll have a much easier time changing with it.

Chris Pine

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This article is part of the CodeSmell Series.