How to determine which architectures are available (Apple M1)?

Code
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I wanted to report back on how I ended up implementing it. I am not saying it is the best way or the only way to do it, but it is the way that makes the most sense for my project/framework. I know that a solution proposed in another thread (and in the 8th edition of the book) is to use $(ARCHS_STANDARD) which gets expanded by Xcode, but I don’t like it because the content of this variable is not available in CMake so I can’t act on it (printing a message, generating the zip archive name, etc…) (see below).

The full source is available on github.

The gist of it:

  • allow to disable universal build if you don’t want it via an option
  • run uname -m to determine the platform hence whether universal build is even an option
  • check whether the generator is Xcode otherwise you can’t do a universal build
  • I also set a variable (JAMBA_ARCHIVE_ARCHITECTURE) representing the build architecture so that it is available in other places for example to determine the name of the zip file generated and also injected in a header in the code (#define). This would be impossible to do with $(ARCHS_STANDARD)…
# Enable/Disable universal build on Apple Silicon
option(JAMBA_ENABLE_XCODE_UNIVERSAL_BUILD "Enable building x86/arm64 universal binary on Apple Silicon" ON)

# Deployment target/architectures for macOS
if(APPLE)
  # set the deployment target if provided
  if(JAMBA_MACOS_DEPLOYMENT_TARGET)
    set(CMAKE_OSX_DEPLOYMENT_TARGET "${JAMBA_MACOS_DEPLOYMENT_TARGET}" CACHE STRING "")
  endif()

  # on macOS "uname -m" returns the architecture (x86_64 or arm64)
  execute_process(
      COMMAND uname -m
      RESULT_VARIABLE result
      OUTPUT_VARIABLE JAMBA_OSX_NATIVE_ARCHITECTURE
      OUTPUT_STRIP_TRAILING_WHITESPACE
  )

  # determine if we do universal build or native build
  if(JAMBA_ENABLE_XCODE_UNIVERSAL_BUILD                     # is universal build enabled?
      AND (CMAKE_GENERATOR STREQUAL "Xcode")                # works only with Xcode
      AND (JAMBA_OSX_NATIVE_ARCHITECTURE STREQUAL "arm64")) # and only when running on arm64
    set(CMAKE_OSX_ARCHITECTURES "x86_64;arm64" CACHE STRING "")
    set(JAMBA_ARCHIVE_ARCHITECTURE "macOS_universal")
    message(STATUS "macOS universal (x86_64 / arm64) build")
  else()
    set(JAMBA_ARCHIVE_ARCHITECTURE "macOS_${JAMBA_OSX_NATIVE_ARCHITECTURE}")
    message(STATUS "macOS native ${JAMBA_OSX_NATIVE_ARCHITECTURE} build")
  endif()

elseif(WIN32)
  # nothing special for windows
  set(JAMBA_ARCHIVE_ARCHITECTURE "win_64bits")
  message(STATUS "Windows native build")
endif()```
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