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Addressed issue #134

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Herb Sutter 2015-10-16 11:11:24 -07:00
parent 67f8609657
commit 0198926d53
1 changed files with 15 additions and 5 deletions
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CppCoreGuidelines.md
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@ -4867,6 +4867,10 @@ To prevent slicing, because the normal copy operations will copy only the base p
It's good to return a smart pointer, but unlike with raw pointers the return type cannot be covariant (for example, `D::clone` can't return a `unique_ptr<D>`. Don't let this tempt you into returning an owning raw pointer; this is a minor drawback compared to the major robustness benefit delivered by the owning smart pointer. It's good to return a smart pointer, but unlike with raw pointers the return type cannot be covariant (for example, `D::clone` can't return a `unique_ptr<D>`. Don't let this tempt you into returning an owning raw pointer; this is a minor drawback compared to the major robustness benefit delivered by the owning smart pointer.
##### Exceptions
If you need covariant return types, return an `owner<derived*>`. See [C.130](#Rh-copy).
##### Enforcement ##### Enforcement
A class with any virtual function should not have a copy constructor or copy assignment operator (compiler-generated or handwritten). A class with any virtual function should not have a copy constructor or copy assignment operator (compiler-generated or handwritten).
@ -5420,27 +5424,33 @@ Readability. Detection of mistakes. Explicit `override` allows the compiler to c
##### Reason ##### Reason
Copying a base is usually slicing. If you really need copy semantics, copy deeply: Provide a virtual `clone` function that will copy the actual most-derived type, and in derived classes return the derived type (use a covariant return type). Copying a base is usually slicing. If you really need copy semantics, copy deeply: Provide a virtual `clone` function that will copy the actual most-derived type and return an owning pointer to the new object, and then in derived classes return the derived type (use a covariant return type).
##### Example ##### Example
class base { class base {
public: public:
virtual base* clone() = 0; virtual owner<base*> clone() = 0;
virtual ~base() = 0;
base(const base&) = delete;
base& operator=(const base&) = delete;
}; };
class derived : public base { class derived : public base {
public: public:
derived* clone() override; owner<derived*> clone() override;
virtual ~derived() override;
}; };
Note that because of language rules, the covariant return type cannot be a smart pointer. Note that because of language rules, the covariant return type cannot be a smart pointer. See also [C.67](#Rc-copy-virtual).
##### Enforcement ##### Enforcement
* Flag a class with a virtual function and a non-user-defined copy operation. * Flag a class with a virtual function and a non-user-defined copy operation.
* Flag an assignment of base class objects (objects of a class from which another has been derived). * Flag an assignment of base class objects (objects of a class from which another has been derived).
### <a name="Rh-get"></a> C.131: Avoid trivial getters and setters ### <a name="Rh-get"></a> C.131: Avoid trivial getters and setters
##### Reason ##### Reason
@ -13336,7 +13346,7 @@ No. These guidelines are about how to best use Standard C++14 + the Concepts Lit
### <a name="Faq-markdown"></a> FAQ.10: What version of Markdown do these guidelines use? ### <a name="Faq-markdown"></a> FAQ.10: What version of Markdown do these guidelines use?
These coding standards are written using [Common Markdown](http://commonmark.org), and `<a>` HTML anchors. These coding standards are written using [CommonMark](http://commonmark.org), and `<a>` HTML anchors.
We are considering the following extensions from [GitHub Flavored Markdown (GFM)](https://help.github.com/articles/github-flavored-markdown/): We are considering the following extensions from [GitHub Flavored Markdown (GFM)](https://help.github.com/articles/github-flavored-markdown/):