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iOS Developer Interview Questions

What are phantom types and when would you use them?

Suggested approach: Phantom types are a type that doesn’t use at least one its generic parameters – they are declared with a generic parameter that isn’t used in their properties or methods.

Even though we don’t use the generic type parameter, Swift does, which means it will treat two instances of our type as being incompatible if their generic type parameters are different. They aren’t used often, but when they are used they help the compiler enforce extra rules on our behalf – they make bad states impossible because the compiler will refuse to build our code.

  Estimated difficulty: Advanced

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Important notes

  • There are over 150 interview questions in the system. Once you've read the question and come up with a suitable answer, try reading my suggested approach and see if it helps you add more detail.
  • These questions are not designed to be hard; a good interviewer is more interested in generating discussion that lets your ability and interests shine through.
  • If you answer a question with "yes" or "no" you've missed the point – interviewers prefer you to provide reasoning, explanation, or detail, so try to elaborate with examples!
  • If you're looking for detailed technical questions about the language, you should try my Swift tests instead – there are multiple challenges that will work your brain hard.
  • For a whole series of coding challenges, I wrote the perfect book for you: Swift Coding Challenges.

Related questions

See the full list of iOS interview questions

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