TITLE: Void * implicit type conversions

PROBLEM: mg@tyrolia.Princeton.EDU (Michael Golan)

Farther, the language designers encourage you to provide a void* 
type conversion; 


RESPONSE: peju@alice.att.com (Peter Juhl)

Could you post a reference to where the C++ language designer(s) has
encouraged people to provide void* type conversions ? I can't find it
anywhere among my papers / books.


RESPONSE: rmartin@rcmcon.com (Robert Martin), 31 Aug 93

I think the origninal statement was a bit too strong.  The void* issue
probably comes from iostreams.  An iostream has a void* converter so
that it can be placed as the expression in a conditional:

	while (cin >> i)
	{
		...
	}

I think even the author of this idiom is aware of the dangers of too
many conversion operators and would not recommend a willy nilly
lemmings off the cliff rampage into lots and lots of conversions.  

However, there are some cases where conversions to void* seem
appropriate, where the advantages appear to outweigh the risks.  Time
will tell if these judgements are correct.  As for iostreams, I have
yet to encounter an error because of the void* conversion.

My favorite iterator convention uses a similar void* conversion so
that I can use the following idiom:

void f(Set<int>& x)
{
  for (Iterator<int> i(x); i; i++)
    cout << *i;
}

The void* operator returns 0 when the iterator has reached the end of
the list.

[ Be very careful about supplying implicit type conversions. They
  basically give the compiler license to silently change your code,
  increasing the chances of causing hard-to-find bugs. -adc ]