cond. op. on ='s LHS

[Dan Bernstein]

In article <331 at smds.UUCP> rh at smds.UUCP (Richard Harter) writes:
> Let's run down the line on this.  First of all the trick of using
> *(cond?&var1:&var2) is not technically legal since the result of the
> ?: is not an lvalue.

Say what? It doesn't matter whether foobiebletch is an lvalue as long as
nobody tries to assign a value to it. Here foobiebletch is a (non-const)
pointer type, so *foobiebletch is an lvalue, and *foobiebletch = x is
fine.

> Secondly the syntax of the condition is, in its own right, ugly.

Yes. I'd write either

 {
  register glorp *addr;
  if (cond) addr = &var1;
  else      addr = &var2;
  *addr = expr;
 }

or

 {
  register glorp temp;
  temp = expr;
  if (cond) var1 = temp;
  else      var2 = temp;
 }

if any of the expressions involved were particularly complex. How else
would the machine do the job anyway?

> There really is a need for
> conditional expressions.

This can be argued. ?: is almost purely syntactic; I don't know any
machine that will optimize a ?: expression better than an equivalent
if-then. Its syntactic benefits are minimal at best.

---Dan