Determining platform at runtime

Using Swift
1

<The title of this post was renamed from " Is this a bug? return statement inside #if os() causes warning " to be more accurate>

Hello, the following code:

import Foundation
func testLinux() {
	#if !os(Linux)
		print("Bailing - not on Linux, this function is not relevant")
		return
	#endif

	//  OK, we're on Linux.
	print("We are on Linux")
}

gives an error:

Code after 'return' will never be executed

Is this a bug? Or should I create a variable which is flipped inside the #if statement and then return later based on that? (edit - even if I do that, the warning is still present.)

2

The correct tool here is to do:

#if !os(Linux)
	print("Bailing - not on Linux, this function is not relevant")
#else
	print("We are on Linux")
#endif

In your example, since all of the diagnostic logic happens after the conditional compilation determines what AST is built, you basically end up with the same AST as if you wrote:

print("Bailing - not on Linux, this function is not relevant")
return
print("We are on Linux")
3

You could do this, maybe:

func testLinux() {
	#if !os(Linux)
		print("Bailing - not on Linux, this function is not relevant")
	#else
		print("We are on Linux")
	#endif
}
4

Thanks - I suppose I was confusing the pre-processor with runtime evaluation.

I was looking for a way to exit the function early depending on platform. I imagine I should instead use an equivalent to the old Classic macOS 'Gestalt'.

Maybe: Apple Developer Documentation

Thanks again. A category error on my part....

5

ProcessInfo reports OS version but that's not very useful.

e.g.
Linux:
OperatingSystemVersion(majorVersion: 4, minorVersion: 19, patchVersion: 0)

macOS Mojave:
"NSOperatingSystemVersion(majorVersion: 10, minorVersion: 14, patchVersion: 6)\n"

I suppose one could use #if canImport(xxx) or assume that we're not using macOS version 4.0.....

Perhaps ProcessInfo.platform() would be a useful method to add.