Why interfaces?

person holding door lever and key

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We should almost always extract interfaces from your service classes because:

  • We should use dependency injection to load and compose implementations: to avoid the need of manually constructing chains of dependent objects and/or to be able to release implementation changes without rebuilding the entire solution, if dependencies are dynamically loaded.
  • We should isolate and test client callers and for this purpose we need mocking; mocking is a lot easier if the call is performed through an interface.
  • Rarely for polymorphism (although this might be their most obvious use): only if really, really needed – I’d say we should always consider composition first; thst would probably save us from much unforeseen trouble!

About Sorin Dolha

My passion is software development, but I also like physics.
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