scope-cpp11: A single header-only scope guard library for C++11 or later

scope-cpp11 is an implementation of scope_exit, scope_success, scope_fail and unique_resource proposed for the C++ standard at by P0052r10.

scope_exit, unique_resource is available in C++11 or later. scope_success and scope_fail are available in C++17 or later (because these require std::uncaught_exceptions()).

Example

#include <scope/scope.hpp>

using namespace scope;

void demo_scope_exit_fail_success_in_p0052() {
    std::ostringstream out{};
    auto lam = [&]{out << "called ";};
    try {
        auto v = scope_exit([&]{out << "always ";});
        auto w = scope_success([&]{out << "not ";}); // not called
        auto x = scope_fail(lam); // called
        throw 42;
    } catch(...) { // v, x called at this point
        auto y = scope_fail([&]{out << "not ";}); // not called
        auto z = scope_success([&]{out << "handled";}); // called
    } // z called at this point
    assert("called always handled" == out.str());
}

void demonstrate_unique_resource_with_stdio_in_p0052() {
    auto fclose = [](auto file){ ::fclose(file); }; // not allowed to take address
    const std::string filename = "hello.txt";
    {   auto file = scope::make_unique_resource(::fopen(filename.c_str(), "w"), fclose);
        ::fputs("Hello World!\n", file.get());
        assert(file.get() != NULL);
    }
    {   std::ifstream input { filename };
        std::string line { };
        getline(input, line);
        assert("Hello World!" == line);
        getline(input, line);
        assert(input.eof());
    }
    ::remove(filename.c_str());
    {   auto file = scope::make_unique_resource_checked(::fopen("nonexistingfile.txt", "r"), (FILE*)NULL, fclose);
        assert(file.get() == NULL);
    }
}

Install

scope-cpp11 is a single header-only library. Copy scope.hpp into your project.

Dependencies

scope-cpp11 depends on the C++ standard library only. (I use catch2 for unit test)

Usage

Refer to P0052r10 for detailed documentation.

Difference from P0052r10

• Header file name is scope.hpp instead of <scope>.
• Namespace is scope:: instead of std::.
• Added make_scope_exit(), make_scope_success(), make_scope_fail(), make_unique_resource() functions. This extension is for C++11/14 that doesn't have a template deduction guide.

Reference

Scope guard concept was proposed by Petru Marginean and Andrei Alexandrescu.

It has been proposed for standardization by P0052r10, and adopted in 2019-03.

Appendix

1. Test status

scope-cpp11 passed the test included in the original proposal.