Swift protocols interview questions

Protocols are central to Swift design, so interviews use them to test how you think about abstraction, testing, and coupling.

What gets asked

Expect questions on protocol-oriented programming, default implementations in extensions, protocols with associated types, and protocols versus class inheritance. Interviewers often ask how you would use a protocol to make a dependency injectable and testable, or when a protocol adds ceremony without real benefit.

Answering with judgment

Frame protocols as contracts that decouple callers from implementations, which makes code testable by letting you swap a real service for a fake. Prefer composition of small protocols over deep inheritance, use default implementations sparingly, and be honest that not every type needs a protocol; premature abstraction is a real cost.

Go deeper than a summary

Share Your Screen works topics like this through in full: 75 solved Swift problems with tests, 9 real case studies, and 7 annotated mock interviews, so you rehearse the live round instead of just reading about it.

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Frequently asked

Protocols or inheritance?

Prefer protocols and composition for flexibility and testability; use class inheritance when you genuinely need shared stored state and an is-a relationship.

How do protocols help testing?

They let you depend on an abstraction and inject a fake or mock in tests, so you can verify behavior without real network, disk, or time dependencies.