Increase Build Time — Faster Builds with Precompiled Bridging Headers

Now reduce build time upto 30%.

The Problem
Every time a Swift file in a mixed-language target is compiled, the Swift compiler parses the project’s bridging header in order to make Objective-C code visible to Swift code. When the bridging header is large and the Swift compiler runs many times — as in a debug configuration — the cost of repeatedly parsing the bridging header can be a substantial part of the overall build time.
Build Setting

In Swift 3.1, you can reduce debug build time by 30% by using the new Swift flag for this issue, It is currently experimental and must be manually enabled; in future releases, if developer feedback indicates it’s working well and providing significant speedup, it will be enabled by default. To try it out in the meantime, install a compiler that supports it, open the build settings for your project and set “Other Swift Flags” to contain the option -enable-bridging-pch.