_____ _        _          _____                         _____
 / ____| |      | |        / ____|                       / ____|_     _
| (___ | |_ __ _| |_ ___  | (___   __ ___   _____ _ __  | |   _| |_ _| |_
 \___ \| __/ _` | __/ _ \  \___ \ / _` \ \ / / _ \ '__| | |  |_   _|_   _|
 ____) | || (_| | ||  __/  ____) | (_| |\ V /  __/ |    | |____|_|   |_|
|_____/ \__\__,_|\__\___| |_____/ \__,_| \_/ \___|_|     \_____|

State Saver C++

Sometimes a certain value has to change only for a limited scope. This class wrapper saves a copy of the current state of some object, and resets the object’s state at destruction time, undoing any change the object may have gone through.

• saver_exit - saves the original variable value and restores on scope exit.

• saver_fail - saves the original variable value and restores on scope exit when an exception has been thrown.

• saver_success - saves the original variable value and restores on scope exit when no exceptions have been thrown.

Features

• C++11
• Header-only
• Dependency-free

Examples

• State Saver on exit

  void Foo(A& a)
    SAVER_EXIT(a);
    ... // Alter state from non-const functions.
    ... // Other code.
    // Original state automatically restored on scope exit.
  }

• State Saver on fail

  void Foo(A& a)
    SAVER_FAIL(a);
    ... // Alter state from non-const functions.
    ... // Other code.
    // Original state automatically restored when an exception has been thrown.
  }

• State Saver on success

  void Foo(A& a)
    SAVER_SUCCESS(a);
    ... // Alter state from non-const functions.
    ... // Other code.
    // Original state automatically restored when no exceptions have been thrown.
  }

Synopsis

Reference

saver_exit

• saver_exit<decltype(object)> state_saver{object}; - creation saver_exit for the object.
• SAVER_EXIT{object}; - macro for creating saver_exit for the object.
• MAKE_SAVER_EXIT(name) {object}; - macro for creating named saver_exit for the object.
• WITH_SAVER_EXIT(object) {/*...*/}; - macro for creating scope with saver_exit for the object.

saver_fail

• saver_fail<decltype(object)> state_saver{object}; - creation saver_fail for the object.
• SAVER_FAIL{object}; - macro for creating saver_fail for the object.
• MAKE_SAVER_FAIL(name) {object}; - macro for creating scope with saver_fail for the object.
• WITH_SAVER_FAIL(object) {/*...*/}; - macro for creating scope with saver_fail for the object.

saver_success

• saver_success<decltype(object)> state_saver{object}; - creation saver_success for the object.
• SAVER_SUCCESS{object}; - macro for creating saver_success for the object.
• MAKE_SAVER_SUCCESS(name) {object}; - macro for creating scope with saver_success for the object.
• WITH_SAVER_SUCCESS(object) {/*...*/}; - macro for creating scope with saver_success for the object.

Interface of state_saver

saver_exit, saver_fail, saver_success implement state_saver interface.

• constructor state_saver(T& object) - construct state_saver with saved object.

• dismiss() - dismiss restore on scope exit.

• restore() - resets the object’s state. Requirements copy operator =.

Requirements to saved object

• POD or object semantic (cannot be reference, function, ...).
• Copy constructor.
• operator= (no-throw one preferred).

Configuration macros

Throwable settings

• STATE_SAVER_NO_THROW_CONSTRUCTIBLE define this to require nothrow constructible.

• STATE_SAVER_MAY_THROW_RESTORE define this to restore may throw exceptions.

• STATE_SAVER_NO_THROW_RESTORE define this to require noexcept restore.

• STATE_SAVER_SUPPRESS_THROW_RESTORE define this to exceptions during restore will be suppressed.

• By default using STATE_SAVER_MAY_THROW_RESTORE.

• STATE_SAVER_CATCH_HANDLER define this to add exceptions handler. If STATE_SAVER_SUPPRESS_THROW_RESTORE is not defined, it will do nothing.

Assignable settings

• STATE_SAVER_FORCE_MOVE_ASSIGNABLE define this to restore on scope exit will be move assigned.

• STATE_SAVER_FORCE_COPY_ASSIGNABLE define this to restore on scope exit will be copy assigned.

• By default using move assignable if noexcept.

Integration

You should add required file state_saver.hpp.

Compiler compatibility

• Clang/LLVM >= 5
• MSVC++ >= 14.0 / Visual Studio >= 2015
• Xcode >= 9
• GCC >= 5

Licensed under the MIT License