[boost] Re: [review results] hash functions accepted

From: Thorsten Ottosen (nesotto_at_[hidden])
Date: 2005-03-22 07:24:48

"Dave Harris" <brangdon_at_[hidden]> wrote in message 
news:memo.764802_at_cix.compulink.co.uk...
| In-Reply-To: <d1mq8d$b5q$1_at_[hidden]>
| nesotto_at_[hidden] (Thorsten Ottosen) wrote (abridged):
| > 7. the hash_ptr<> suggestion is better done with general indirected
| > function
|
| Did I miss where this was discussed?

No, I don't think so. I'm bringing it up now, because
I think the proposed hash_ptr and equal_ptr is a bad idea.

| To recap, we were talking about
| adding something like:
|
|    template<typename T>
|    struct hash_ptr {
|        size_t operator()(const T *p) const {
|            return hash_value( *p );
|        }
|    };
|
|    template<typename T>
|    struct equal_ptr {
|        bool operator()( const T *a, const T *b ) const {
|            return *a == *b;
|        }
|    };
|
| to the hash library for use as, eg:
|
|   unordered_set< MyType *, hash_ptr<MyType>, equal_ptr<MyType> >
|
| What do you mean by using a "general indirected function" instead?

There is a small utility in the Pointer Container library which is more 
general
that hash_ptr ect. You can simply say

unordered_set< MyType*, indirect_fun< boost::hash<MyType> >, indirect_fun< 
std::equal<MyType> > >  set;

for the rare cases where the index is a pointer.

-Thorsten