Compiler warning when a class breaks rule-of-three (five)

Question

Is it possible to trigger compiler warning when a class breaks rule-of-three (or rule-of-five)?

This feature sounds easy to implement and is very useful in safety critical software but I can't find it anywhere in documentation or Google search results.

This might be idealist claptrap but IMHO it's far better to build your classes in such a way that you never need to implement the functions required for the rule-of-three or the rule-of-five. — Bathsheba, Dec 07 '16 at 11:56
@Bathsheba absolutely agree. If you're not using rule of zero then your code is not sufficiently decomposed. — Richard Hodges, Dec 07 '16 at 11:57
I personally would not like to have a check for Rule of five as I'm not sure it's a good guideline. Please check this discussion by Howard Hinnant: http://stackoverflow.com/a/38687106/1989995 — alexeykuzmin0, Dec 07 '16 at 12:06
Rule of zero is great but only works because people are following rule of five elsewhere. Someone has gotta implement the special member functions eventually. — Ryan Haining, Apr 29 '19 at 16:30

score 5 · Accepted Answer · answered Dec 07 '16 at 12:34

5

You can use the compiler flag -Weffc++ for GCC

answered Dec 07 '16 at 12:34

Swapnil

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-Weffc++ does find some interesting issues, but it doesn't find "rule of five" violations. I'm using current gcc from the gcc-8-branch. Neither does current clang. – proski May 01 '18 at 21:35
1

seconded. `-Weffc++` does not catch this – Ryan Haining May 16 '18 at 06:01
1

[example of clean compilation with that flag](https://wandbox.org/permlink/JTOCTyhNlapSnjzt) – Ryan Haining May 16 '18 at 14:25

score 3 · Answer 2 · answered May 16 '18 at 06:05

clang-tidy can catch such mistakes. Given this file:

// badstyle.cpp
class Type {
  Type(const Type&) { }

  ~Type() { }
};

And this command:

$ clang-tidy badstyle.cpp -checks=cppcoreguidelines-*

My output is:

badstyle.cpp:2:7: warning: class 'Type' defines a non-default destructor and a 
copy constructor but does not define a copy assignment operator, a move constructor
or a move assignment operator [cppcoreguidelines-special-member-functions]
class Type {
  ^

score 2 · Answer 3 · answered Dec 07 '16 at 11:54

2

Visual Studio 2017 RC states to have some "Checkers for enforcing the C++ Core Guidelines". Since the "Rule of five" is one of the most easily checked rules, I believe it's implemented.

answered Dec 07 '16 at 11:54

alexeykuzmin0

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Compiler warning when a class breaks rule-of-three (five)

3 Answers3