darkerstar/libindi-scope

An implementation of the proposed (P0052) C++ <scope> header

libindi-scope

An implementation of the proposed (P0052) C++ <scope> header

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Overview

C++ standards proposal P0052 describes a new standard library header <scope> that includes scope guards. Scope guards provide ad-hoc RAII functionality, which is particularly useful when using C library facilities in modern C++ code.

This project is all about the single header scope.hpp, which aims to be a drop-in replacement for <scope> (except that everything is in the indi namespace, rather than std). The goal is that you can take the scope.hpp header and drop it into any project to be able to use P0052’s scope guards. (And if and when <scope> is standardized, you can simply replace the include directive and namespace, and everything should work exactly the same.)

Library

The following is only a brief overview of the provided library facilities. For details, see the revision of P0052 that is currently tracked by this project.

Scope guards

The header scope.hpp provides 3 scope guards:

• scope_exit
• scope_success
• scope_fail

All three scope guards can be initialized with a function or reference to a function, which is then called when the scope guard is destroyed. The only difference between the three scope guards are the conditions when the function is called.

Scope guard	When function is called
scope_exit	Whenever the scope guard is destroyed.
scope_success	Only if the scope guard is destroyed normally (not via stack unwinding).
scope_fail	Only if the scope guard is destroyed via stack unwinding.

Example:

auto f()
{
    auto const s1 = scope_exit   {[] { std::cout << "exit!"; }};
    auto const s2 = scope_success{[] { std::cout << "good!"; }};
    auto const s3 = scope_fail   {[] { std::cout << "fail!"; }};

    // [...]

    // "fail!" will be printed ONLY if an exception was thrown above.
    // "good!" will be printed ONLY if an exception was *NOT* thrown.
    // "exit!" will be printed, no matter what happened above.
}

All scope guards also have a release() member function, that prevents the wrapped function from being called under any circumstances.