Re: m68k gcc/egcs question

In comp.compilers James Jones <jejones@microware.com> wrote:
: cp = &(c = 10);


An example of the above from some real code I had to deal with once upon a
time:


// If key doesn't exist, value is unmodified.
void getkey(const char *key, int &value) {...};
...
{
        int value1;
        int value2;


        getkey("key1", value1 = 42);
        getkey("key2", value2 = 17);
        // etc...
}


Metrowerks' compiler of the time spit out a warning on this about
passing a temporary into a non-const ref. The programmer (and I use
the term loosely) who wrote the code insisted that doing the
assignment in the function argument was perfectly valid well defined
C++. Metrowerks insisted that their compiler was correct because the
C++ specification does not say the assignment operator returns its
left operand as an lvalue (i.e. a ref to the left operand), but
rather that the assignment must return an lvalue of the type of its
left operand with the value of its left operand.


After asking a number of experts and posting in comp.std.c++, I
decided that Metrowerks interpretation of the standard is correct but
that almost everybody was surprised by this and thought assignment
always returned a ref to the left hand operand. (Of course the above
code is pretty dubious, but it was a major effort convincing its
author to fix it.)


-Z-

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