Hi folks,

I'm attempting to parse C++ using the grammar given in the DWP of 4/28/95, and I've run
into an anomaly that I'm hoping you can help me understand.

The code looks like this:

class testB : testA {
  testB& operator=(const testB& l) {
    return (testB&) ((testA&)*this = (const testA&)l);
  }
};

The strange thing is that "(testA&)*this" looks like a cast-expression, but the grammar
won't allow a cast-expression as the left-hand side of an assignment-expression.  Yet,
the code does compile, at least using Sun's C++.  I'm able to parse it by changing the
definition of assignment-expression from:

assignment-expression:
  conditional-expression
  unary-expression assignment-operator assignment-expression
  throw-expression

to:

assignment-expression:
  conditional-expression
  unary-expression assignment-operator assignment-expression
  cast-expression assignment-operator assignment-expression
  throw-expression

This'll probably suffice for our purposes (reverse engineering), but of course it isn't
correct ("(int) x = 5;" is still a syntax error).  I am curious about the reasoning
behind this special-case extension of the lvalue, and whether it's in the standard, and
how it might be defined more explicitly.  Help?  Thanks in advance,
  -James-

------------------------------------------------------------------------------
James Powell  james@advancedsw.com                Go ahead, squeeze the wheeze
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James Powell <james@advancedsw.com> writes:

>I'm attempting to parse C++ using the grammar given in the DWP of 4/28/95
[...]
>assignment-expression:
>  conditional-expression
>  unary-expression assignment-operator assignment-expression
>  throw-expression

In the November 96 draft, this is

  assignment-expression:
   conditional-expression
   logical-or-expression assignment-operator assignment-expression
   throw-expression

--
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WWW: <http://www.cs.mu.oz.au/~fjh>   |  of excellence is a lethal habit"
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