Code Smell 28 — Setters
The first exercise junior programmers do. IDEs, tutorials and senior developers keep teaching them this anti-pattern.
Problems
- Mutability
- Information Hiding
- Anemic Models
- Fail Fast
- Integrity
- Duplicated Code
Solutions
- Avoid Setters
- Set essential attributes on private initialization.
Sample Code
Wrong
Mutation brings lots of problems
Information Hiding Violated
Right
Detection
First step will be to forbid public attributes (if language allows them).
Secondly, we will search for methods setXXXX(), analyzing method structure (should be an assignment to attribute xxxx).
We should not forbid methods setting accidental state since this is valid. They should not be named setters since they ask the object to change, but they don’t set anything.
Examples
- DTOs
Exceptions
Setting attributes is safe for non-essential attributes.
Essential behavior is what distinguishes one object from another.
It is related to behavior and not data. It’s not a primary key definition.
Some patterns, like Builder require setting the parts in a controlled, incremental way. Validations are done at the end and the real entity metaphor requires it.
Setting accidental values has many drawbacks and considerations already mentioned.
Tags
- Mutation
- Information Hiding
Conclusion
Creating incomplete and anemic objects is a very bad practice violating
mutability, fail fast principle and real world bijections.
Relations
More Info
Here is the full discussion on Setters
Object-oriented programming languages support encapsulation, thereby improving the ability of software to be reused, refined, tested, maintained, and extended. The full benefit of this support can only be realized if encapsulation is maximized during the design process.
Rebecca Wirfs-Brock
This article is part of the CodeSmell Series.
