Re: [boost] [functional] How to avoid a dependency on functional?

Subject: Re: [boost] [functional] How to avoid a dependency on functional?
From: Peter Dimov (lists_at_[hidden])
Date: 2015-01-09 15:17:30

Beman Dawes wrote:
> Filesystem has a dependency on <boost/functional/hash_fwd.hpp> in order to 
> supply this:
>
>   inline std::size_t hash_value(const path& x)
>   {
> # ifdef BOOST_WINDOWS_API
>     std::size_t seed = 0;
>     for(const path::value_type* it = x.c_str(); *it; ++it)
>       hash_combine(seed, *it == '/' ? L'\\' : *it);
>     return seed;
> # else   // BOOST_POSIX_API
>     return hash_range(x.native().begin(), x.native().end());
> # endif
>   }
...
> Is there any recommended way to avoid the functional dependency?

In this specific case, I would forward-declare hash_combine and hash_range. 
I already submitted a pull request against array along the same lines, which 
Marshall graciously accepted.

Had 'hash' been in its own module, I would consider simply including 
hash.hpp, rather than relying on forward declarations, as 'hash' should be a 
very lightweight module.