Re: [boost] [hash] documentation issues (was [TR1 Review] TR1 Formal Review Beginning)

From: Daniel James (daniel_at_[hidden])
Date: 2005-10-09 04:58:21

Alexander Nasonov wrote:
> That's not quite right. For example
> 
> #include <iostream>
> #include <boost/functional/hash.hpp>
> 
> struct Base
> {
>     bool operator==(Base) const { return true; }
> };
> 
> std::size_t hash_value(Base)
> {
>    return 0; // Base has no state
> }
> 
> struct Derived : Base
> {
>    int dummy;
>    bool operator==(Derived other) const { return dummy == other.dummy; }
> };

OK, I thought you meant something else. It seems to me that in this 
case, hash_value(Base) is a part of Base's interface - so any class that 
derives from it should take it into account. It also appears that Base 
wasn't really designed for derivation (despite its name ;), and it's 
generally a bad idea to derive from such classes. I guess that's a bit 
of a cop out answer, but this is more of a problem with the way the 
derivation is done than Boost.Hash itself.

What I should do, is add some documentation about using Boost.Hash with 
class inheritance. I'll try to do that soon-ish.

What do you think about having a macro to disable the extensions? Am I 
right in thinking that your main concern is that the extensions are in 
Boost.TR1?

Sorry for the late reply,

Daniel