What is Prefix.pch file in Xcode?

Question

So many developers are adding various convenience macros to the Prefix.pch. But my question is what is that Prefix.pch file.

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Answer 1

History:

#include => #import => .pch

#include vs #import

Precompiled Headers - prefix.pch

#include vs @import has a disadvantage - slow build time because a compiler must parse and compile as many times as many .h files were imported.

Precompiled header file - .pch - collects the common headers. When this file is precompiled ones it can be used in source files which speeds up a build time.

Let's take a look at Prefix.pch sample:

#ifdef __OBJC__
    #import 
    #import 
#endif

To add .pch file go to Build Settings:

Developer has to manage .pch file that imposes additional costs for supporting it.

The next step is @import[About]