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C++ 17 & C++ 20 error-handling and utility extensions.

Overview

STX is a collection of libraries and utilities designed to make working with C++ easier and less error-prone.

Libraries

Features

  • Efficient Result<T, E> (error-handling) and Option<T> (optional-value) implementation with monadic methods
  • Unignorable error-types
  • Fail-fast (Abandonment/ Fatal failure) via panic s
  • Reporting via Report ( SpanReport and FixedReport )
  • Runtime panic hooks
  • Panic backtraces
  • Signal backtraces ( SIGSEGV , SIGILL , and SIGFPE )
  • Backtrace library
  • Portable, suitable, and easily-adoptable for embedded systems, real-time systems, safety-critical systems, and operating systems
  • Easy debugging
  • Easy to use and hard to misuse API
  • Exception-free, RTTI-free, and memory allocation free ( no-std )
  • Space and time deterministic error-handling
  • Deterministic value lifetimes
  • Eliminates repitive code and abstractable error-handling logic code via monadic extensions
  • Fast success and error return paths
  • Modern and clean API
  • Well-documented
  • Extensively tested
  • Functions using only Result and Option for error and optional value handling are callable from C code as they are unions.

Basic Examples

Option

#include <iostream>

#include "stx/option.h"

using stx::Option, stx::Some, stx::None;

auto safe_divide(double numerator, double denominator) -> Option<double> {
  if (denominator == 0.0) return None;
  return Some(numerator / denominator);
}

int main() {
  safe_divide(5.0, 2.0).match(
      [](auto value) { std::cout << "Result: " << value << std::endl; },
      []() { std::cout << "Cannot divide by zero" << std::endl; });
}

Result

#include <array>
#include <cinttypes>
#include <iostream>

#include "stx/result.h"

using std::array, std::string_view;
using namespace std::literals;

using stx::Result, stx::Ok, stx::Err;

enum class Version { V1 = 1, V2 = 2 };

auto parse_version(array<uint8_t, 6> const& header) -> Result<Version, string_view> {
  switch (header.at(0)) {
    case 1:
      return Ok(Version::V1);
    case 2:
      return Ok(Version::V2);
    default:
      return Err("Unknown Version"sv);
  }
}

int main() {
  parse_version({2, 3, 4, 5, 6, 7}).match([](auto version){
    std::cout << "Version: " << static_cast<int>(version) << std::endl;
  }, [](auto error){
    std::cout << error  << std::endl;
  });

}

Propagating Errors with TRY_OK

TRY_OK assigns the successful value to its first parameter version if parse_version returned an Ok , else propagates the error value.

// As in the example above
auto parse_version(array<uint8_t, 6> const& header) -> Result<Version, string_view>;

auto parse_data(array<uint8_t, 6> const& header) -> Result<uint8_t, string_view> {
  TRY_OK(version, parse_version(header));
  return Ok(version + header[1] + header[2]);
}

int main() {
  auto parsed = parse_data({2, 3, 4, 5, 6, 7}).unwrap();

  std::cout << parsed << std::endl;
}

You can also add const/volatile attributes to TRY_OK 's assigned value, i.e:

auto parse_data(array<uint8_t, 6> const& header) -> Result<uint8_t, string_view> {
  TRY_OK(const version, parse_version(header));
  return Ok(version + header[1] + header[2]);
}

Guidelines

  • Result and Option will only work in constexpr context (compile-time error-handling) in C++ 20, to check if you can use it as constexpr check if the macros STX_RESULT_CONSTEXPR and STX_OPTION_CONSTEXPR are set to 1, for an example see constexpr_test .

  • To ensure you never forget to use the returned errors/results, raise the warning levels for your project ( -Wall -Wextra -Wpedantic on GNUC-based compilers, and /W4 on MSVC)

  • Some methods like map , unwrap, or_else, and most of Result and Option's monadic methods consume the stored value and thus the Result or Option has to be destroyed as its lifetime has ended. For example:

    Say we define a function named safe_divide as in the example above, with the following prototype:

auto safe_divide(float n, float d) -> Option<float>;

And we call:

float result = safe_divide(n, d).unwrap(); // compiles, because 'safe_divide' returns a temporary
Option option = safe_divide(n, d);
float result = option.unwrap();  // will not compile, because 'unwrap' consumes the value and is only usable with temporaries (as above) or r-value references (as below)

Alternatively, suppose the Option or Result is no longer needed, we can obtain an r-value reference:

Option option = safe_divide(n, d);
float result  = std::move(option).unwrap(); // will compile, the value is moved out of 'option' , 'option' should not be used any more

NOTE: Just as any moved-from object, Option and Result are not to be used after a std::move ! (as the objects will be left in an unspecified state).

  • Result and Option do not make any implicit copies of the contained object as they are designed as purely forwarding types, this is especially due to their primary purpose as return channels in which we do not want duplication nor implicit copies of the returned values.

To make explicit copies:

Option option = safe_divide(n, d);
float result = option.clone().unwrap(); // note that 'clone()' explicitly makes a copy of the 'Option'

We can also obtain an l-value reference to copy the value:

Option option = safe_divide(n, d);
float result = option.value(); // note that 'value()' returns an l-value reference and 'result' is copied from 'option''s value in the process

float result = safe_divide(n, d).value(); // this won't compile as 'value' always returns an l-value reference, use 'unwrap()' instead
  • All methods of Result and Option pass r-value/l-value references to their invocable parameters.

Benchmarks

Release Mode ( -O3 )

Target Real Time CPU Time Iterations
Variant/SuccessPath 0.392 ns 0.392 ns 1000000000
Exception/SuccessPath 0.386 ns 0.386 ns 1000000000
Result/SuccessPath 0.381 ns 0.381 ns 1000000000
C-Style/SuccessPath 0.387 ns 0.386 ns 1000000000
Variant/FailurePath 0.408 ns 0.408 ns 1000000000
Exception/FailurePath 2129 ns 2129 ns 317810
Result/FailurePath 0.384 ns 0.384 ns 1000000000
C-Style/FailurePath 0.384 ns 0.383 ns 1000000000

Build Requirements

  • CMake
  • Make or Ninja Build
  • C++ 17 or C++ 20 Compiler
  • Git
  • Doxygen and Graphviz (for documentation)

Tested-on Compilers

Compiler x86-64 arm-linux aarch64-linux
Clang-10 YES NO NO
Clang-9 YES YES YES
GCC-9 YES YES YES
GCC-8 YES YES YES
GCC-7 YES NO NO
MSVC-2019 YES NO NO

CMake Configuration Options

  • STX_BUILD_SHARED - Build STX as a shared library
  • STX_BUILD_TESTS - Build test suite
  • STX_BUILD_DOCS - Build documentation
  • STX_BUILD_BENCHMARKS - Build benchmarks
  • STX_SANITIZE_TESTS - Sanitize tests if supported. Builds address-sanitized, thread-sanitized, leak-sanitized, and undefined-sanitized tests
  • STX_OVERRIDE_PANIC_HANDLER - Override the global panic handler
  • STX_ENABLE_BACKTRACE - Enable the backtrace library
  • STX_ENABLE_PANIC_BACKTRACE - Enable panic backtraces. It depends on the backtrace library ( STX_ENABLE_BACKTRACE )
  • STX_VISIBLE_PANIC_HOOK - Make runtime panic hooks attachable when loaded as a dynamic library (i.e. device drivers)

License

MIT License