Re: Questions about chapter 11 (Operator Overloading) of TC++PL.

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Tue, 23 Oct 2007 11:02:20 -0400

Message-ID:

<ffl2ds$2ur$1@news.datemas.de>

Wayne Shu wrote:

On 10 23 , 5 09 , anon <a...@no.no> wrote:

Wayne Shu wrote:

Hi everyone, I am reading B.S. 's TC++PL (special edition).
When I read chapter 11 Operator Overloading, I have two questions.

1. In subsection 11.2.2 paragraph 1, B.S. wrote "In particular,
operator =, operator[], operator(), and operator-> must be nonstatic
member function; this ensures that their first operands will be
lvalues". I know that these operators must be nonstatic member
functions, but why this ensure their first operands will be lvalues?
e.g.
class foo
{
int i;
public:
foo & operator = (int ii) { i = ii; return *this; }

The first operant is ii.

No.

};

foo bar() { return foo(); }

bar() = 10;
here bar() is a rvalue.

The first operant is 10, not bar()

No.

10 is a rvalue too.

Yes, but...

To 'anon':

When talking about binary operators (operators with two operands),
the "first" operand is the one that is shown/written to the *left*
when the operator is *being used*. So, when looking at the
expression

a = b

while discussing the assignment operator, 'a' is the _first_
operand and 'b' is the _second_. In C++ it translates so that the
*first* operand is the object for which the function operator= is
called, and the *second* is the actual argument of that function.

In the case above, whatever the subexpression 'bar()' yields would
be the _first_ operand. '10' would be the _second_ operand.

Just making sure we're using the correct terminology.

And, sorry, I don't have the answer to the original question.

V
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