Don't make data members `const` or references in a copyable or movable type

Reason

const and reference data members are not useful in a copyable or movable type, and make such types difficult to use by making them at least partly uncopyable/unmovable for subtle reasons.

Example; bad

class bad {
    const int i;    // bad
    string& s;      // bad
    // ...
};

The const and & data members make this class "only-sort-of-copyable" -- copy-constructible but not copy-assignable.

Note

If you need a member to point to something, use a pointer (raw or smart, and gsl::not_null if it should not be null) instead of a reference.

Enforcement

Flag a data member that is const, &, or && in a type that has any copy or move operation.