Design Patterns · Senior · Question 58 of 75

Two packages: `checkout` needs to send emails, and `notifications` implements email sending. Following DIP, who owns the interface?

✓Correct answer: The consumer (checkout) defines the interface it needs; notifications implements it
2notifications defines it, and checkout depends on its implementation
3A global shared utils package

Explanation

High-level policy then doesn't depend on low-level details, and implementations can be swapped or faked in tests.

Further reading

Wikipedia: Dependency inversion principle ↗

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