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Protocol extensions
Learn protocol extensions in Swift through a focused explanation, a dedicated topic-specific example, an engineering boundary, and a mastery check.
protocol extensions is an atomic Swift topic inside Classes and Protocols. The example uses the named construct directly so you can see its syntax, data flow, and observable behavior.
Read the code by locating the exact feature named protocol extensions, then trace the value before and after that feature runs. This lesson is intentionally isolated from neighboring topics: changing identifiers alone would not reproduce the same behavior because the construct itself is different.
Topic-specific example
protocol Greet{};extension Greet{func hi(){print("hi")}};struct Person:Greet{};Person().hi()For protocol extensions, test the boundary that makes the feature meaningful: invalid input, an empty value, a missing branch, lifecycle/cleanup, or a type/runtime constraint. Do not infer correctness only from the happy path.