Jean-Philippe DUFRAIGNE 1b4f8100ef Allow iterator copy for lambda in transformed and filtered ...

Lambda has no default constructor nor a copy or move assignment.

range\test\adaptors.cpp is checking that produced ranges are copiable,
but it is not doing so the for lambda, or lambda like objects.

default_constructible_unary_fn uses an optional for default
construction.
I extended it to use its emplace facility to copy assign non copy
assignable types.
(see boost::optional 'Type Requierment':  'If T is not MoveAssignable,
it is still possible to reset the value of optional<T> using function
emplace():')

2016-10-23 23:27:31 +01:00

..

boost

Allow iterator copy for lambda in transformed and filtered

2016-10-23 23:27:31 +01:00