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Add exceptions to F.15, F.16, and F.18 for shared_ptr types (#2010)

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Currently these guidelines conflict with R.34, R.35, and R.36.

This conflict has led to confusion, where it's unclear which
guidelines to prefer for `shared_ptr` types.

In a [previous
PR](https://github.com/isocpp/CppCoreGuidelines/pull/1989) I proposed
preferring the "F" series of guidelines.  This PR takes the opposite
approach and prefers the "R" guidelines for `shared_ptr` types.

I don't feel strongly about which guidelines to prefer, I just want to make
sure the guidelines are internally consistent.
This commit is contained in:
Russell McClellan
2023-01-19 17:16:39 -05:00
committed by GitHub
parent fa31c19979
commit 1ba3371a0d
1 changed files with 14 additions and 0 deletions
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CppCoreGuidelines.md
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@@ -2978,6 +2978,11 @@ Use the advanced techniques only after demonstrating need, and document that nee
For passing sequences of characters see [String](#SS-string). For passing sequences of characters see [String](#SS-string).
##### Exception
To express shared ownership using `shared_ptr` types, rather than following guidelines F.16-21,
instead follow [R.34](#Rr-sharedptrparam-owner), [R.35](#Rr-sharedptrparam), and [R.36](#Rr-sharedptrparam-const).
### <a name="Rf-in"></a>F.16: For "in" parameters, pass cheaply-copied types by value and others by reference to `const` ### <a name="Rf-in"></a>F.16: For "in" parameters, pass cheaply-copied types by value and others by reference to `const`
##### Reason ##### Reason
@@ -3029,6 +3034,11 @@ If you need the notion of an optional value, use a pointer, `std::optional`, or
* (Simple) ((Foundation)) Warn when a parameter passed by reference to `const` has a size less or equal than `2 * sizeof(void*)`. Suggest passing by value instead. * (Simple) ((Foundation)) Warn when a parameter passed by reference to `const` has a size less or equal than `2 * sizeof(void*)`. Suggest passing by value instead.
* (Simple) ((Foundation)) Warn when a parameter passed by reference to `const` is `move`d. * (Simple) ((Foundation)) Warn when a parameter passed by reference to `const` is `move`d.
##### Exception
To express shared ownership using `shared_ptr` types, instead follow [R.34](#Rr-sharedptrparam-owner) or [R.36](#Rr-sharedptrparam-const),
depending on whether or not the function unconditionally takes a reference to the argument.
### <a name="Rf-inout"></a>F.17: For "in-out" parameters, pass by reference to non-`const` ### <a name="Rf-inout"></a>F.17: For "in-out" parameters, pass by reference to non-`const`
##### Reason ##### Reason
@@ -3107,6 +3117,10 @@ For example:
// use p ... possibly std::move(p) onward somewhere else // use p ... possibly std::move(p) onward somewhere else
} // p gets destroyed } // p gets destroyed
##### Exception
If the "will-move-from" parameter is a `shared_ptr` instead follow [R.34](#Rr-sharedptrparam-owner) and pass the `shared_ptr` by value.
##### Enforcement ##### Enforcement
* Flag all `X&&` parameters (where `X` is not a template type parameter name) where the function body uses them without `std::move`. * Flag all `X&&` parameters (where `X` is not a template type parameter name) where the function body uses them without `std::move`.