[MacPorts] #67545: gnucash @5.0_1: error: no template named 'unary_function' in namespace 'std' (was: gnucash @5.0_1: doesn't build on macos 10.11 and other)

[MacPorts]

#67545: gnucash @5.0_1: error: no template named 'unary_function' in namespace
'std'
----------------------+----------------------
  Reporter:  tenzap   |      Owner:  drkp
      Type:  defect   |     Status:  assigned
  Priority:  Normal   |  Milestone:
 Component:  ports    |    Version:  2.8.1
Resolution:           |   Keywords:
      Port:  gnucash  |
----------------------+----------------------

Comment (by ryandesign):

 The Portfile sets `compiler.cxx_standard 2017` and I see `-std=c++17` in
 the log.

 The Internet tells me `std::unary_function` is deprecated in C++11 and
 removed in C++17.

 So this is not a situation of El Capitan being too old. On the contrary,
 it's a situation where the compiler we're using to support those old
 systems (Clang 16 in this case) is so new that it has removed support for
 `unary_function` which boost, which gnucash depends on, uses. I think the
 Xcode clang versions we're using on newer macOS versions already support
 C++17 but aren't new enough that they removed `unary_function`, but they
 will start failing too once we update to newer versions of Xcode.

 gnucash is using boost 1.71 which is old. The
 [https://github.com/boostorg/config/pull/440 upstream PR about this issue]
 has been merged so it should either be fixed in the latest boost or the
 next boost to be released; gnucash could switch to newer boost.

-- 
Ticket URL: <https://trac.macports.org/ticket/67545#comment:3>
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