When an object changes its state the best solution is to change the attribute, isn't it?
Problems
Mutability
Attributes polluting
Setters
Solutions
1 - Model states as mathematical set inclusion.
2 - State is accidental, take it away from the object.
Examples
- State diagrams
Sample Code
Wrong
Right
Detection
If we want to be extreme, we should consider every setter to be a potential state change. Linters can warn us. But we might end up getting too many false positives.
Exceptions
Over Design
Performance issues (if a serious benchmark supports it).
Tags
- Mutation
Conclusion
This technique is very elegant but can lead to over design. For example changing a visual component its color should be a counterexample to this smell.
We should be aware and very caution like with any other smell.
They are hints and not rigid rules.
Relations
More info
Credits
First make the change easy (warning: this might be hard), then make the easy change.
Kent Beck
This article is part of the CodeSmell Series.