Re: reference to non-const temporary

Thu, 27 Jul 2006 13:32:45 CST
Ethan Eade wrote:

I'm curious -- why aren't temporaries allowed to be passed as non-const
references? It seems slightly arbitrary, since non-const methods can be
called on them anyway.

It is arbitrary. IIRC, the rule was added to the language because
programmers were getting unexpected results from code like:

  void add_one( long& x ) { x = x + 1; }

  int i = 1;
  add_one( i );
  assert( i == 2 );

At first glance, it's easy to imagine that add_one( i ) will operate on
i, but, of course, it doesn't -- it operates on a temporary, the result
of the implicit conversion from int to long.

It's possible to say, "Well, don't make that mistake." But I gather
that, in real life, programmers *did* make this mistake, often enough
that the "const rule" was added in order to catch it.

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