Scope Guard

Implementation of Scope Guards (scope_exit, scope_success, scope_fail) and unique_resource as proposed in P0052R10.

• scope_exit: Executes a callable when the current scope is left
• scope_success: Executes a callable only if the scope exits normally (no exception)
• scope_fail: Executes a callable only if an exception is thrown during the scope
• unique_resource: RAII wrapper that owns a resource and calls a deleter on destruction or reset
• make_unique_resource_checked(): Helper that creates a unique_resource and releases it if the resource equals an invalid value

Compatibility

This implementation conforms to P0052, except:

Namespace

The namespace sr is used instead of std.

Filenames

The filenames contain a .h extension. To enable the compatible header as specified in the document the CMake option SCOPEGUARD_ENABLE_COMPAT_HEADER can be used. This will generate and install an additional header named scope (without file extension).

Standardisation progress

P0052 has been adopted (2019-03) and is in the Library Fundamentals v3 now.

Documentation

• P0052R10 – Generic Scope Guard and RAII Wrapper for the Standard Library (P. Sommerlad, A. L. Sandoval, E. Niebler, D. Krügler)
• N4853 – C++ Extensions for Library Fundamentals, Version 3 (T. Köppe)

Usage Examples

scope_exit

#include "scope_exit.h"

void example() {
    sr::scope_exit guard([] {
        std::cout << "Cleanup executed when scope exits\n";
    });

    // Do work ...
}

scope_success

#include "scope_success.h"

void example() {
    sr::scope_success guard{[] {
        std::cout << "Success: no exception was thrown\n";
    }};

    // Do work that might throw ...
}

scope_fail

#include "scope_fail.h"

void example() {
    sr::scope_fail guard{[] {
        std::cout << "Failure: an exception was thrown\n";
    }};

    // do work that might throw ...
}

unique_resource

#include "unique_resource.h"

class Resource {
    // ...
};

void example() {
    sr::unique_resource resource{
        Resource{"Example resource"},
        [](Resource r) {
            // Delete r
            std::cout << "Resource deleted\n";
    }};

    auto& res = resource.get();
    // Use resource ...
}

make_unique_resource_checked()

#include "unique_resource.h"

class Resource {
    // ...
};

void example() {
    auto resource = sr::make_unique_resource_checked(
        Resource{"invalid"},  // invalid value
        [](Resource r) {
            // Delete r
            std::cout << "Resource deleted\n";
    });
    // Resource is released if it equals the invalid value

    auto& res = resource.get();
    // Use resource ...
}

License

MIT License

Copyright (c) 2017-2026 offa

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