hash template specializations require BOOST_HAS_TR1_HASH work-around

[Jim Bell <jim@…>]

The TR1 docs show the templated hash struct being in namespace std::tr1.

But putting a hash template specialization in std::tr1 doesn't work, at least in cases where BOOST_HAS_TR1_HASH isn't defined.

This is broken for both MinGW-gcc-4.4 and MSVC-8 (VS2005).

See the attached files:

• TR1_hash_break.cpp doesn't compile for either platform.
• TR1_hash_workaround.cpp compiles for both.

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MSVC-8: Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 14.00.50727.762 for 80x86

Copyright (C) Microsoft Corporation. All rights reserved.

TR1_hash_break.cpp TR1_hash_break.cpp(21) : error C2888: 'boost::hash<my_key>' : symbol cannot be defined within namespace 'tr1'

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MinGW gcc-4.4: TR1_hash_break.cpp:17: error: specialization of 'template<class T> struct boost::hash' in different namespace F:\boost\MinGW-32\trunk\boost/boost/tr1/functional.hpp:127: error: from definition of 'template<class T> struct boost::hash' TR1_hash_break.cpp:19: error: definition of 'size_t boost::hash<my_key>::operator()(const my_key&) const' is not in namespace enclosing 'boost::hash<my_key>'

[Jim Bell <jim@…>]

Er, forgive the old-style casts on lines 20/25. They ought to be "static_cast<std::size_t>(r)". (Didn't inspect that borrowed code closely enough.)

[John Maddock]

(In [69508]) Fix typo in inverse_gausian.qbk. Fixes #5254.

[Jim Bell <jim@…>]

This ticket concerns tr1/functional.hpp, not libs/math/doc/... Perhaps you typo'd the ticket #.

[anonymous]

Grrr, serves me right for working on two at once....

[anonymous]

Will fix this shortly by making std::tr1::hash a thin wrapper inheriting from boost::hash, but.... your code will still break on MSVC-10 as there std::tr1::hash is actually an alias for std::hash, and there's nothing we can do at our end to fix that, other than to say don't do that'' :-(

[John Maddock]

(In [69520]) Make std::tr1::hash a thin wrapper around boost::hash so folks can specialise it. Fixes #5254.

[Jim Bell <jim@…>]

I'd love to see the docs, at the point of use (i.e., doc/html/boost_tr1/subject_list.html#boost_tr1.subject_list.hash), mention these portability caveats where we know about them. Do I ask too much?