Re: [Boost-users] [multi_index] problem with hashed index

On Wed, 21 Mar 2007 21:40:54 +0200, JOAQUIN LOPEZ MU?Z wrote:

[...]Hi again, I answered too fast, the answer above is more or less correct but there's more to it: you have overloaded hash_value for shared_ptr<foo>s so as to use the pointed to foo objects:

std::size_t hash_value(const shared_ptr<foo> &f) { std::size_t seed = 0; boost::hash_combine(seed, f->i); boost::hash_combine(seed, f->j); return seed; }

So far so good; but the hashed index depends not only on the hash functor, but also on an equality predicate, which is by default (in this case)

std::equal_to,

which compares pointers, not foo objects. Hence the problem. Rather than overloading std::equal_to, which breaks the natural equality semantics of shared_ptr, my advice is that you change the key of the hashed index to:

indexed_by >

as suggested in my previous post, and write the overload of hash_value for foo, not for shared_ptr<foo>:

std::size_t hash_value(const foo &f) { std::size_t seed = 0; boost::hash_combine(seed, f.i); boost::hash_combine(seed, f.j); return seed; }

Does this work? Please report back,

Thanks, it worked. I also had to define the comparison operator == for foo though. Boris