DEV Community

Cover image for Code Smell 47 - Diagrams
Maxi Contieri
Maxi Contieri

Posted on • Updated on • Originally published at

Code Smell 47 - Diagrams

Diagrams are not code. They cannot be a code smell. They are just Diagram Smells.


  • Maintainability

  • Trash code

  • Code Duplication

  • Diagrams focus only on structure (accidental) and not behavior (essential).


  1. Use diagrams only to communicate ideas with other humans.

  2. Program on your favorite IDE.

  3. Thrash all diagrams. Even the ones generated from the source code.

  4. Trust your tests. They are alive and well maintained.

  5. Use Domain Driven Design technique.

Sample Code





We can remove all code annotations and forbid them by policy.



Designing is a contact sport. We need to prototype and learn from our running models.

Papers and JPGs don't run. They live in the utopic world where everything works smoothly.

CASE was a very hot trend back in the 90s.
No good system was developed with these tools.


More info

Code Wizards




Photo by Nick Seagrave on Unsplash

The Diagram is Not the Model. The model is not the diagram. It is an abstraction, a set of concepts and relationships between them.

Eric Evans

Top comments (1)

darkwiiplayer profile image
𒎏Wii 🏳️‍⚧️

UML is a joke. It's the attempt of people who don't like programming to avoid it and do code-free software engineering. The problem is that this ultimately just removes the main difficulty of figuring out the implementation details and creates a world of make-believe where programs don't need to actually compile or execute.

The obvious exception is, of course, when discussing different implementation approaches, as a short-term thing, but not as documentation.

As you pointed out, most of these diagrams express how something is implemented (structure), not its behaviour. I hadn't considered it from this perspective yet, but you're definitely right. A good diagram would express primarily what code does, not how it does it. However, some diagrams manage to convey at least a bit of behaviour as well, but even then writing a simple markdown document can do a much better job.

Trust your tests. They are alive and well maintained.

Maybe one could use diagrams to describe these tests. At least on the surface this seems like it could work.