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