Detection and versioning of operating systems, compilers, architecture, and SIMD extensions are traditionally done using messy preprocessor macros.

SPY is a C++20 library that gathers this information and provides a constexpr compatible interface. This replaces #ifdef spaghetti with clean, compile-time control flow.

SPY turns compile-time detection into simple boolean checks:

#include <spy/spy.hpp>
#include <iostream>

int main()
{
  // Check Compiler
  if constexpr( spy::compiler == spy::clang_ )
  {
    std::cout << "Optimizing with Clang version " << spy::compiler.version << "\n";
  }

  // Check Architecture
  if constexpr( spy::architecture == spy::amd64_ )
  {
    std::cout << "Running on x86-64\n";
  }

  // Check SIMD capabilities (hierarchical)
  if constexpr( spy::simd_instruction_set >= spy::avx2_ )
  {
    std::cout << "AVX2 or better is available\n";
  }
}

SPY detects and versions a wide range of environments:

You can grab the standalone single-header file from the standalone branch.

wget https://github.com/jfalcou/spy/raw/standalone/spy.hpp

SPY has no dependencies, making it easy to fetch compile-time:

include(FetchContent)
FetchContent_Declare(
  spy
  GIT_REPOSITORY [https://github.com/jfalcou/spy.git](https://github.com/jfalcou/spy.git)
  GIT_TAG        v2.0.0 # Replace with latest tag
)
FetchContent_MakeAvailable(spy)

target_link_libraries(your_target PRIVATE spy::spy)

CPMAddPackage(
  NAME spy
  GITHUB_REPOSITORY jfalcou/spy
  GIT_TAG v2.0.0
)
target_link_libraries(your_target PRIVATE spy::spy)

The complete API documentation can be found here.

• Our CppCon 2019 Ligthning talk slides
• Our CppCon 2019 Ligthning talk video

This project is licensed under the Boost Software License 1.0.