Re: Iterators for basic_string/vector

[Nathan Myers <ncm@best.com>]

> > To get that, they must be distinct types so that 
> > trying to do something that should be illegal can in fact be illegal.  
> 
> I think a lot of this ambiguity will be resolved if specific examples
> could be generated. Can you provide some code to illustrate things that
> "should be illegal" that are permitted in the current implementation? Both
> illegalities between raw pointers and iterator classes, and interator to
> const_iterator conversions? I would appreciate it. 

Here is an example for implementations where iterators are really pointers:

  std::vector<char> v[1];
  std::vector<char>::iterator vi = v.begin();
  std::string::iterator si = vi;  // oops, string iter points into a vector!

Here is an example where const_iterator is the same type as iterator:

  const std::vector<int> v[1];
  std::vector<int>::const_iterator cvi = v.const_begin();
  std::vector<int>::iterator = cvi;
  *cvi = 0;  // oops, just clobbered a "const" vector!

In each case, errors of a type that are normally caught by the type 
system slip through because the library facility fails to model a 
builtin type correctly.

Nathan Myers
ncm@cantrip.org