karma indirect_iterator returns reference to temporary

[Louis Dionne <louis.dionne92@…>]

Hello,

The indirect_iterator in boost/spirit/home/karma/detail/indirect_iterator.hpp returns a reference to a temporary in at least one corner case. The compiler will issue a warning, but it's still UB.

I attached the minimal code to reproduce the behavior as well as a fix. Without the fix, it will print crap and issue a warning (on Clang and GCC).

What happens: I create a transformed_range, which uses a transform_iterator under the hood. Since the function performing the transformation returns by value, the the iterator_traits<transform_iterator>::reference type is NOT the same as iterator_traits<transform_iterator>::value_type const&, hence the return of a reference to a temporary.

My setup:

gcc version 4.7.2 clang version 3.2 boost-trunk@82516

Best,

Louis Dionne

[Louis Dionne <louis.dionne92@…>]

fix for the issue

[Louis Dionne <louis.dionne92@…>]

minimal code to reproduce the issue

[Louis Dionne <louis.dionne92@…>]

Sorry for the mis-formatting of my setup. Should've previewed the ticket before posting!

My setup:

gcc version 4.7.2

clang version 3.2

boost-trunk@82516

[Hartmut Kaiser]

(In [82521]) Fix #7900: karma indirect_iterator returns reference to temporary