Refactoring Day 5 : Pull Up Field

Today we look at a refactoring that is similar to the Pull Up method. Instead of a method, it is obviously done with a field instead!

   1: public abstract class Account
   2: {
   3: }
   4:  
   5: public class CheckingAccount : Account
   6: {
   7:     private decimal _minimumCheckingBalance = 5m;
   8: }
   9:  
  10: public class SavingsAccount : Account
  11: {
  12:     private decimal _minimumSavingsBalance = 5m;
  13: }

In this example, we have a constant value that is duplicated between two derived classes. To promote reuse we can pull up the field into the base class and rename it for brevity.

   1: public abstract class Account
   2: {
   3:     protected decimal _minimumBalance = 5m;
   4: }
   5:  
   6: public class CheckingAccount : Account
   7: {
   8: }
   9:  
  10: public class SavingsAccount : Account
  11: {
  12: }

 

This is part of the 31 Days of Refactoring series. For a full list of Refactorings please see the original introductory post.

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About Sean Chambers

I am a Senior software developer from Palm Coast, Florida. An advocate of Domain Driven Design, Behavior Driven Development, creator of FluentMigrator and community activist. I am married to my beautiful wife Erin and am the proud father of two wonderful children. I currently reside at ACI, a local insurance industry/mortgage software company that excels in creating solutions using Agile methodologies.
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  • http://thomaseyde.blogspot.com Thomas Eyde

    I don’t like that refactoring, kind of. I think it’s incomplete. It’s all about preferences, though, but I think protected fields are a code smell:

    - if you need access to a base class field, you probably have some kind of feature envy. Try Templated Method or something similar.

    - There is nothing in the subclass telling you that this field exists, you just have to know it. It hurts readability.

  • Ed

    I would say pulling anything up into a base class should be done with caution

    It’s likely to lead to a fragile base class. Favour composition over inheritence, using inheritence as a mechanism for reuse iis picking the option with the tightest coupling from the word go

  • nfma

    @Thomas Eyde

    Some refactorings are just steps on other bigger refactorings. Pull up method might make sense in the context…