fast_scope_guard.hpp

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#pragma once
 
#include <type_traits>
#include <utility>
 
/// @file userver/utils/fast_scope_guard.hpp
/// @brief @copybrief utils::FastScopeGuard
 
USERVER_NAMESPACE_BEGIN
 
namespace utils {
 
/// @ingroup userver_universal userver_containers
///
/// @brief a helper class to perform actions on scope exit
///
/// The lambda argument must be explicitly marked as `noexcept`. Only use
/// FastScopeGuard if it's proven that the lambda body is `noexcept`, otherwise
/// use ScopeGuard.
///
/// Usage example:
/// @snippet universal/src/utils/fast_scope_guard_test.cpp  FastScopeGuard
///
/// @see ScopeGuard for type-erasure and throwing functor support
template <typename Callback>
class FastScopeGuard final {
public:
    static_assert(std::is_nothrow_move_constructible_v<Callback>);
 
    static_assert(
        std::is_nothrow_invocable_v<Callback&&>,
        "If the functions called in the body of the lambda are all 'noexcept', "
        "please mark the lambda itself as 'noexcept'. If however, the contents "
        "are not 'noexcept', use 'ScopeGuard' instead of 'FastScopeGuard'."
    );
 
    static_assert(std::is_void_v<std::invoke_result_t<Callback&&>>, "Return type of Callback function should be void");
 
    static_assert(std::is_nothrow_destructible_v<Callback>, "Callback function destructor should be noexcept");
 
    constexpr explicit FastScopeGuard(Callback callback) noexcept : callback_(std::move(callback)) {}
 
    constexpr FastScopeGuard(FastScopeGuard&& other) noexcept
        : callback_(std::move(other.callback_)), is_active_(std::exchange(other.is_active_, false)) {}
 
    constexpr FastScopeGuard& operator=(FastScopeGuard&& other) noexcept {
        if (this != &other) {
            callback_ = std::move(other.callback_);
            is_active_ = std::exchange(other.is_active_, false);
        }
        return *this;
    }
 
    ~FastScopeGuard() {
        if (is_active_) std::move(callback_)();
    }
 
    constexpr void Release() noexcept { is_active_ = false; }
 
private:
    Callback callback_;
 
    // should be optimized out if 'Release' is not called
    bool is_active_{true};
};
 
}  // namespace utils
 
USERVER_NAMESPACE_END