In article <JASON.94Apr15181458@deneb.cygnus.com>
           jason@cygnus.com "Jason Merrill" writes:

>>       class Avoidable
>>       {
>>       public:
>>               operator void() { cout << "Avoidable" << endl; }
>>       };
>
>The current Working Paper disallows this code:
>
>"If conversion-type-id is void or cv-qualified void, the program is
>ill-formed."
>
>So explicitly casting to void cannot differ semantically from simply
>ignoring the value.
>
>Jason
>

Thanks for this information. It should stop a lot of unnecessary 'fun'.
--
Kevlin Henney

In a nutshell, is a discarded value in an expression statement
considered to be implicitly cast to void, as in Algol-68, or not?

 #include <iostream.h>

 class Avoidable
 {
 public:
  operator void() { cout << "Avoidable" << endl; }
 };

 int main()
 {
  Avoidable thing;
  (void) thing; // 1
  thing;  // 2
  return 0;
 }

So are statements 1 and 2 equivalent? Trial by compiler(s) says they are
not, but is this truly the case or an oversight? The ARM does not seem
to mention how discarded values are treated.
--
Kevlin Henney

>>>>> Kevlin Henney <kevlin@wslint.demon.co.uk> writes:

>  class Avoidable
>  {
>  public:
>   operator void() { cout << "Avoidable" << endl; }
>  };

The current Working Paper disallows this code:

"If conversion-type-id is void or cv-qualified void, the program is
ill-formed."

So explicitly casting to void cannot differ semantically from simply
ignoring the value.

Jason