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Last active Mar 14, 2016
What would you like to do?

Adding an Platform-testing Build Configuration Test

  • Proposal: SE-00XX
  • Author(s): Erica Sadun
  • Status: TBD
  • Review manager: TBD


This proposal introduces an if platform(...) test to determine whether code is running on a platform family, such as Apple, Windows, Unix, etc.

This proposal was discussed on-list in the Adding an Platform-testing Build Configuration Test thread.


As Swift expands to a growing developer base and to new platforms, the existing suite of configuration tests begins to show strain. Shortcuts taking advantage of current limitations introduce fragility.

For example, testing #if os(iOS) || os(OSX) || os(watchOS) || os(tvOS) to determine whether code is running on an Apple platform may miss new platform targets and #if !os(Linux) may introduce errors as Swift extends to other non-Apple platforms, such as Windows.

Testing specifically for an Apple, Unix, or Windows platform will enable the Swift development team to move past potentially fragile tests. Dmitri Gribenko writes, "There's a direction that we want to move to a unified name for the libc module for all platform, so "can import Darwin" might not be a viable long-term strategy."

Detail Design

#if platform(platform-name)

I propose a minimum suite of Apple, Windows, Linux, and Unix, where Unix will be true on both Apple and Linux targets.

Current Art

Swift currently supports the following configuration tests:

  • The literals true and false
  • The os() function that tests for OSX, iOS, watchOS, tvOS, Linux, Windows, and FreeBSD
  • The arch() function that tests for x86_64, arm, arm64, i386, powerpc64, and powerpc64le
  • The swift() function that tests for specific Swift language releases, e.g. swift(>=2.2)

Alternatives Considered

There are no alternatives considered.


Dmitri Gribenko:

It is not that I'm saying that there is no good use case, it is just that they are not obvious to me. Here's something I could imagine happening:

#if platform(Unix)
use system()
#else if platform(Windows)
use CreateProcessEx
#error "unknown platform"

But I'm not sure that "Unix-like" and "Windows-like" are precise enough to write the kinds of checks you would want to write in low-level code.

See thread

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