import is a preprocessor mechanism in Objective C (as well as C and C++). When file A #import file B, B is basically copy and pasted into A and processed. When you have many unnecessary #import statements, building an app can take longer than it needs to.

Use @class statements to declare classes where possible in your header files (.h) and put #import statements in your implementation files (.m) instead.

This applies to #include too.

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