Re: [Boost-users] C++11, boost::filesystem::path, no std::hash specialization

Hi Nate, On Sun, Dec 2, 2012 at 11:46 PM, Nathan Crookston < nathan.crookston@gmail.com> wrote:

Hi Benjamin,

On Sun, Dec 2, 2012 at 1:57 PM, Benjamin Kircher < benjamin.kircher@gmail.com> wrote:

...

I cannot use boost::filesystem::path with an e.g. unordered_set because std::hash seems not to be specialized for this type. Is this intended? Should I file a bug? Or am I completely misguided?

I can't comment on whether filesystem::path should be extended to work with boost hash, but I wanted to point out that you could supply your own hashing object (not boost hash, but using hash_combine) without needing to do anything in the boost namespace. That would work now and in the possible future where filesystem::path supports boost::hash.

See < http://www.boost.org/doc/libs/1_52_0/doc/html/unordered/hash_equality.html>. The patch Daniel James attached to the ticket you referenced is probably a good starting point for implementing something like that.

thanks for the kind reply. I found out that boost::filesystem already provides a function hash_value(const path&) which does exactly what you pointed out (it uses hash_combine/hash_range internally). I was then able to provide my own specialization of std::hash with: #include #include namespace std { template<> struct hashboost::filesystem::path { size_t operator()(const boost::filesystem::path& p) const { return boost::filesystem::hash_value(p); } }; } Benjamin