问题
In an attempt to optimize the build time of my app I've added the following to my OTHER_SWIFT_FLAGS:
OTHER_SWIFT_FLAGS =
-Xfrontend -warn-long-expression-type-checking=75
-Xfrontend -warn-long-function-bodies=75
I got a warnings for this specific type checking being slow, and I cannot figure out if I can help the compiler in some way here.
var delay: TimeInterval = TimeInterval(index) * 0.05
Any suggestions what can be done to speed up the compile time for such basic arithmetic operations up?
I'm running Xcode 11.5 with Swift 5
Also tried explicitly casting the number to TimeInterval, which shouldn't be needed as all numbers are Doubles by default.
回答1:
The compiler performs type checks. If you have a long expression, it takes time. Sometimes when the expression is too long, you even get an error as:
The compiler is unable to type-check this expression in reasonable time; try breaking up the expression into distinct sub-expressions
try something like
var delay: TimeInterval = TimeInterval(index) * TimeInterval(0.05)
回答2:
In your build settings, under 'Swift Compiler - General' check the 'Reflection Metadata Level' and try setting it to 'None'.
Since upgrading to Xcode 11.4, I had a project jump from compiling in around 20 seconds to compiling in around 6 - 7 minutes.
I noticed that it only happened in Debug builds, which is strange because Release builds perform more optimizations and should really take longer to compile. I eventually traced the slow builds back to the 'Reflection Metadata Level' setting. It is set to 'All' for 'Debug' builds by default.
This might be a bug in the Swift compiler that's included in Xcode 11.4 and later, because this setting never caused a problem for me in earlier releases. (It started happening with Swift compiler version 5.2.)
来源：https://stackoverflow.com/questions/62641269/why-does-a-simple-swift-arithmetic-operation-compile-so-slow