Best way to hash_combine a bool?

From: John Maddock (jz.maddock_at_[hidden])
Date: 2021-06-05 17:02:35

What's the best way to combine a hash value with a bool?

Specifically, if you're generating a hash value for a class which has a 
one member a bool.  Normally I would just boost::hash_combine all the 
class members together, but doing that with a bool member leads to:

1>d:\data\boost\boost\boost\multiprecision\detail\hash.hpp(20,88): 
warning C4805: '^': unsafe mix of type 'T' and type 'size_t' in operation
1>Â Â Â Â Â Â Â  with
1>Â Â Â Â Â Â Â  [
1>Â Â Â Â Â Â Â Â Â Â Â  T=bool
1>Â Â Â Â Â Â Â  ]

Followed by a long instantiation backtrace (this is from 
Boost.Multiprecision).

Since there's only one bool in this class, I could just apply a unary ~Â  
to the value when the bool is true, but obviously that wouldn't work for 
classes with multiple bool's.  Should we modify hash_combine for this 
use case?

Cheers, John.

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