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https://github.com/Neargye/scope_guard
Scope Guard & Defer C++
https://github.com/Neargye/scope_guard
c-plus-plus c-plus-plus-11 cplusplus cplusplus-11 cpp cpp11 defer-operator header-only no-dependencies scope-guard single-file
Last synced: 3 months ago
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Scope Guard & Defer C++
- Host: GitHub
- URL: https://github.com/Neargye/scope_guard
- Owner: Neargye
- License: mit
- Created: 2018-04-05T09:51:02.000Z (over 6 years ago)
- Default Branch: master
- Last Pushed: 2024-01-23T11:56:48.000Z (10 months ago)
- Last Synced: 2024-05-09T07:35:47.100Z (6 months ago)
- Topics: c-plus-plus, c-plus-plus-11, cplusplus, cplusplus-11, cpp, cpp11, defer-operator, header-only, no-dependencies, scope-guard, single-file
- Language: C++
- Homepage:
- Size: 319 KB
- Stars: 143
- Watchers: 9
- Forks: 15
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
- AwesomeCppGameDev - scope_guard
README
[](https://github.com/Neargye/scope_guard/releases)
[](LICENSE)
# Scope Guard & Defer C++
Scope Guard statement invokes a function with deferred execution until surrounding function returns in cases:
* scope_exit - executing action on scope exit.
* scope_fail - executing action on scope exit when an exception has been thrown.
* scope_success - executing action on scope exit when no exceptions have been thrown.
Program control transferring does not influence Scope Guard statement execution. Hence, Scope Guard statement can be used to perform manual resource management, such as file descriptors closing, and to perform actions even if an error occurs.
## Features
* C++11
* Header-only
* Dependency-free
* Thin callback wrapping, no added std::function or virtual table penalties
* No implicitly ignored return, check callback return void
* Defer or Scope Guard syntax and "With" syntax
## [Examples](example)
* [Scope Guard on exit](example/scope_exit_example.cpp)
```cpp
std::fstream file("test.txt");
SCOPE_EXIT{ file.close(); }; // File closes when exit the enclosing scope or errors occur.
```
* [Scope Guard on fail](example/scope_fail_example.cpp)
```cpp
persons.push_back(person); // Add the person to db.
SCOPE_FAIL{ persons.pop_back(); }; // If errors occur, we should roll back.
```
* [Scope Guard on success](example/scope_success_example.cpp)
```cpp
person = new Person{/*...*/};
// ...
SCOPE_SUCCESS{ persons.push_back(person); }; // If no errors occur, we should add the person to db.
```
* Custom Scope Guard
```cpp
persons.push_back(person); // Add the person to db.
MAKE_SCOPE_EXIT(scope_exit) { // Following block is executed when exit the enclosing scope or errors occur.
persons.pop_back(); // If the db insertion fails, we should roll back.
};
// MAKE_SCOPE_EXIT(name) {action} - macro is used to create a new scope_exit object.
scope_exit.dismiss(); // An exception was not thrown, so don't execute the scope_exit.
```
```cpp
persons.push_back(person); // Add the person to db.
auto scope_exit = make_scope_exit([]() { persons.pop_back(); });
// make_scope_exit(A&& action) - function is used to create a new scope_exit object. It can be instantiated with a lambda function, a std::function, a functor, or a void(*)() function pointer.
// ...
scope_exit.dismiss(); // An exception was not thrown, so don't execute the scope_exit.
```
* With Scope Guard
```cpp
std::fstream file("test.txt");
WITH_SCOPE_EXIT({ file.close(); }) { // File closes when exit the enclosing with scope or errors occur.
// ...
};
```
## Synopsis
### Reference
#### scope_exit
* `scope_exit make_scope_exit(F&& action);` - return scope_exit with the action.
* `SCOPE_EXIT{action};` - macro for creating scope_exit with the action.
* `MAKE_SCOPE_EXIT(name) {action};` - macro for creating named scope_exit with the action.
* `WITH_SCOPE_EXIT({action}) {/*...*/};` - macro for creating scope with scope_exit with the action.
#### scope_fail
* `scope_fail make_scope_fail(F&& action);` - return scope_fail with the action.
* `SCOPE_FAIL{action};` - macro for creating scope_fail with the action.
* `MAKE_SCOPE_FAIL(name) {action};` - macro for creating named scope_fail with the action.
* `WITH_SCOPE_FAIL({action}) {/*...*/};` - macro for creating scope with scope_fail with the action.
#### scope_success
* `scope_success make_scope_success(F&& action);` - return scope_success with the action.
* `SCOPE_SUCCESS{action};` - macro for creating scope_success with the action.
* `MAKE_SCOPE_SUCCESS(name) {action};` - macro for creating named scope_success with the action.
* `WITH_SCOPE_SUCCESS({action}) {/*...*/};` - macro for creating scope with scope_success with the action.
#### defer
* `DEFER{action};` - macro for creating defer with the action.
* `MAKE_DEFER(name) {action};` - macro for creating named defer with the action.
* `WITH_DEFER({action}) {/*...*/};` - macro for creating scope with defer with the action.
### Interface of scope_guard
scope_exit, scope_fail, scope_success implement scope_guard interface.
* `dismiss()` - dismiss executing action on scope exit.
#### Throwable settings
* `SCOPE_GUARD_NOTHROW_CONSTRUCTIBLE` define this to require nothrow constructible action.
* `SCOPE_GUARD_MAY_THROW_ACTION` define this to action may throw exceptions.
* `SCOPE_GUARD_NO_THROW_ACTION` define this to require noexcept action.
* `SCOPE_GUARD_SUPPRESS_THROW_ACTIONS` define this to exceptions during action will be suppressed.
* By default using `SCOPE_GUARD_MAY_THROW_ACTION`.
* `SCOPE_GUARD_CATCH_HANDLER` define this to add exceptions handler. If `SCOPE_GUARD_SUPPRESS_THROW_ACTIONS` is not defined, it will do nothing.
### Remarks
* If multiple Scope Guard statements appear in the same scope, the order they appear is the reverse of the order they are executed.
```cpp
void f() {
SCOPE_EXIT{ std::cout << "First" << std::endl; };
SCOPE_EXIT{ std::cout << "Second" << std::endl; };
SCOPE_EXIT{ std::cout << "Third" << std::endl; };
... // Other code.
// Prints "Third".
// Prints "Second".
// Prints "First".
}
```
## Integration
You should add required file [scope_guard.hpp](include/scope_guard.hpp).
## References
* [Andrei Alexandrescu "Systematic Error Handling in C++"](https://channel9.msdn.com/Shows/Going+Deep/C-and-Beyond-2012-Andrei-Alexandrescu-Systematic-Error-Handling-in-C)
* [Andrei Alexandrescu “Declarative Control Flow"](https://youtu.be/WjTrfoiB0MQ)
## Licensed under the [MIT License](LICENSE)