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0009 - Composition over inheritance

ID:ADR-0009
Status:ACCEPTED
Published:2022-07-25

Context and Problem Statement​

We currently rely heavily on inheritance for our Angular applications. While this seemed like a natural decision at the time since it allowed us to quickly share code between different areas. It has also lead to tight coupling and therefore difficulty in understanding the impact a change will have. It also encourages large page-level components.

Considered Options​

  • Do nothing - Maintain the status quo, not really an option.
  • Prefer composition over inheritance - Split up components into small components that do one thing and one thing only. Keep components thin, and share functionality primarily using Services.

Decision Outcome​

Chosen option: Prefer composition over inheritance

Positive Consequences​

  • Thinner components
  • Better understanding of the impact a change has since it will now be isolated to a single component only.

Negative Consequences​

  • Inheritance tends to be well understood.