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lvalues [was: curly-brace-aphobic?]

Steven D. Majewski sdm7g at virginia.edu
Tue Jan 30 17:37:04 EST 2001 
I used to do that in VAX C all the time 
(i.e. functions returning lvalues):

  a = pop();
  b = pop();
  push() = a + b ;

Then I think ANSI C disallowed it.

Then I think gcc put it back as an extension. 

Don't know for sure -- since then, portability concerns have taught
me to code more conservatively. 

-- Steve M. 


On Tue, 30 Jan 2001, Rainer Deyke wrote:

> "Quinn Dunkan" <quinn at groat.ugcs.caltech.edu> wrote in message
> news:slrn97cu0u.eti.quinn at groat.ugcs.caltech.edu...
> > If C++ allows 'f(x) = y;', then C++ is truly weird.  What is *that*
> supposed
> > to mean?  'f(x)' returns a value, and assigning to a value makes no sense.
> > You assign to variables, not values.  I could understand '*(f(x)) = y;',
> but
> > the only way I can see to get 'f(x) = y;' to do what you want is to have
> 'f'
> > return an lvalue.  Icon does stuff like that, but it has an excuse: it's
> icon.
> > Just out of curiosity, what is the type of the C++ 'f' function above (and
> > don't say "cpp macro" :) ?  It's likely C++'s idea of assignment is one
> I'm
> > not familiar with.
> 
> 'f' here is a function that returns a reference:
> 
> int& f(int);
> 
> This is particularily useful when implementing 'operator[]':
> 
> struct array {
>   int data[5];
>   int& operator[](int n) { return data[n]; }
> };
> 
> array a;
> a[0] = 5;
> a.operator[](0) = 5; // This statement is equivalent to the one above it.
> 
>
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