Weak Linking

When you compile a program that uses external libraries or frameworks, the last step (or a step near the end, at least) is to hook up all of the functions, etc. you use in your program to their implementations in the libraries. This is called “linking”.1

A while back, Apple realized that when they added new features to their frameworks (usually with the release of each new OS version), people might want to take advantage of them, but remain backwards-compatible with old OSs. So they added a feature called weak linking. Apple wasn’t the first to realize that…

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