Re: Why the copy assignment operator is written to return non-const reference to this?

From:

Kai-Uwe Bux <jkherciueh@gmx.net>

Newsgroups:

comp.lang.c++

Date:

Sun, 23 Nov 2008 21:32:09 -0500

Message-ID:

<492a122a$0$17070$6e1ede2f@read.cnntp.org>

Daniel T. wrote:

"Andrew Koenig" <ark@acm.org> wrote:

"joseph cook" <joecook@gmail.com> wrote:

Is this a hard and fast rule? No. I don't expect you'll get any
grief or find any dangerous dragons down the corridor for returning
const ref.

Not true. If you define a class with a copy assignment operator that
returns a const ref, your class does not meet the requirements for an
element type for an STL container. So...

    class Mine {
    // ...
    public:
    const Mine& operator=(const Mine&);
    };

    std::vector<Mine> v; // Undefined behavior -- Mine does not
    meet
the requirements for std::vector

Now I'm confused. As I understand it, the language doesn't require op=
to return any particular type. Stroustrup in "TC++PL" often declares it
to return void...

It's not the language but the Assignable requirement from containers. Table
64 from [23.1./4] requires the return type of t = u to be T&.

Best

Kai-Uwe Bux