deferred

Library for creating deferred evaluation expressions in C++23.

deferred provides:

• functions to declare constants and variables,
• functions to create deferred evaluation expressions from functions,
• deferred-enabled commonly used operators.

Requirements

• C++23 capable compiler.
• CMake 3.28.1 and higher.

Compilers tested:

• Clang 16.0.0 (macOS)
• GCC 13.3.0 (Ubuntu)
• MSVC 19.44 (Windows)

Building

Standard CMake build process:

mkdir build
cd build
cmake ..
cmake --build .

Installation

The library is header-only. You can:

1. Copy the include/deferred directory to your project.
2. Install via CMake:

   cmake --install build --prefix /path/to/install

3. Use as a sub-project in CMake:

   add_subdirectory(deferred)
   target_link_libraries(my_target PRIVATE deferred::deferred)

Documentation

Generate documentation with Doxygen:

# From the build directory
cmake --build . --target documentation

The output will be in the build/html directory.

Usage

// examples/trivial/main.cpp
#include <iostream>
#include <deferred/deferred.hpp>
    
int main()
{
  auto v = deferred::variable<int>();
  auto x = deferred::constant(2);
  auto y = deferred::constant(3);

  auto expression = (v * x) + y;
  
  v = 10;
  
  auto res = expression();
  std::cout << res << "==" << (10 * 2) + 3 << '\n';
  return 0;
}

Examples can be found in the examples/ directory. They are compiled by default.

Testing

Tests are written using Catch2 v3. To run tests after building:

ctest --output-on-failure

Known Issues

• Using callable objects and functions with side-effects in invoke() and if_then_else() will result in a constant expression, assignable to constant_.
• Using deferred with other expression template based classes (e.g., std::valarray) may not be possible.