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doc: cleanup and references in C++ guide
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PR-URL: #23650
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
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refack authored and MylesBorins committed Nov 29, 2018
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Showing 1 changed file with 34 additions and 23 deletions.
57 changes: 34 additions & 23 deletions CPP_STYLE_GUIDE.md
Original file line number Diff line number Diff line change
Expand Up @@ -192,40 +192,39 @@ class FancyContainer {

### Use `nullptr` instead of `NULL` or `0`

What it says in the title.
Further reading in the [C++ Core Guidelines][ES.47].

### Ownership and Smart Pointers

"Smart" pointers are classes that act like pointers, e.g.
by overloading the `*` and `->` operators. Some smart pointer types can be
used to automate ownership bookkeeping, to ensure these responsibilities are
met. `std::unique_ptr` is a smart pointer type introduced in C++11, which
expresses exclusive ownership of a dynamically allocated object; the object
is deleted when the `std::unique_ptr` goes out of scope. It cannot be
copied, but can be moved to represent ownership transfer.
`std::shared_ptr` is a smart pointer type that expresses shared ownership of a
dynamically allocated object. `std::shared_ptr`s can be copied; ownership
of the object is shared among all copies, and the object
is deleted when the last `std::shared_ptr` is destroyed.

Prefer to use `std::unique_ptr` to make ownership
transfer explicit. For example:
* [R.20]: Use `std::unique_ptr` or `std::shared_ptr` to represent ownership
* [R.21]: Prefer `unique_ptr` over `shared_ptr` unless you need to share
ownership

Use `std::unique_ptr` to make ownership transfer explicit. For example:

```cpp
std::unique_ptr<Foo> FooFactory();
void FooConsumer(std::unique_ptr<Foo> ptr);
```
Never use `std::auto_ptr`. Instead, use `std::unique_ptr`.
Since `std::unique_ptr` has only move semantics, passing one by value transfers
ownership to the callee and invalidates the caller's instance.
Don't use `std::auto_ptr`, it is deprecated ([Reference][cppref_auto_ptr]).
## Others
### Type casting
- Always avoid C-style casts (`(type)value`)
- `dynamic_cast` does not work because RTTI is not enabled
- Use `static_cast` for casting whenever it works
- `reinterpret_cast` is okay if `static_cast` is not appropriate
- Use `static_cast<T>` if casting is required, and it is valid
- Use `reinterpret_cast` only when it is necessary
- Avoid C-style casts (`(type)value`)
- `dynamic_cast` does not work because Node.js is built without
[Run Time Type Information][]
Further reading:
* [ES.48]: Avoid casts
* [ES.49]: If you must use a cast, use a named cast
### Using `auto`
Expand Down Expand Up @@ -316,13 +315,25 @@ exports.foo = function(str) {

#### Avoid throwing JavaScript errors in nested C++ methods

When you have to throw the errors from C++, try to do it at the top level and
not inside of nested calls.
When you need to throw a JavaScript exception from C++ (i.e.
`isolate()->ThrowException()`) prefer to do it as close to the return to JS as
possible, and not inside of nested C++ calls. Since this changes the JS
execution state doing it closest to where it is consumed reduces the chances of
side effects.

Using C++ `throw` is not allowed.
Node.js is built [without C++ exception handling][], so code using `throw` or
even `try` and `catch` **will** break.


[C++ Core Guidelines]: http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines
[Google C++ Style Guide]: https://google.github.io/styleguide/cppguide.html
[Google’s `cpplint`]: https://github.com/google/styleguide
[errors]: https://github.com/nodejs/node/blob/master/doc/guides/using-internal-errors.md
[ES.47]: http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-nullptr
[ES.48]: http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-casts
[ES.49]: http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-casts-named
[R.20]: http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rr-owner
[R.21]: http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rr-unique
[Run Time Type Information]: https://en.wikipedia.org/wiki/Run-time_type_information
[cppref_auto_ptr]: https://en.cppreference.com/w/cpp/memory/auto_ptr
[without C++ exception handling]: https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_exceptions.html#intro.using.exception.no

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