We've recently been evaluating a move from boost 1.38 to 1.42 [MSVC71], and we had some code that breaks down to the following: [1] struct T {}; [2] std::auto_ptr<T> ap; [3] boost::shared_ptr<T> sp = ap; Line [3] stopped compiling because of the 'explicit' introduced (in shared_ptr.hpp) at line [L] (below).
From smart_ptr/shared_ptr.hpp:
[A] template<class Y> [B] explicit shared_ptr(std::auto_ptr<Y> & r): px(r.get()), pn() [C] { [D] Y * tmp = r.get(); [E] pn = boost::detail::shared_count(r); [F] boost::detail::sp_enable_shared_from_this( this, tmp, tmp ); [G] } [H] [I]#if !defined( BOOST_NO_SFINAE ) && !defined( BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION ) [J] [K] template<class Ap> [L] explicit shared_ptr( Ap r, typename boost::detail::sp_enable_if_auto_ptr<Ap, int>::type = 0 ): px( r.get() ), pn() [M] { [N] typename Ap::element_type * tmp = r.get(); [O] pn = boost::detail::shared_count( r ); [P] boost::detail::sp_enable_shared_from_this( this, tmp, tmp ); [Q] } The fix is trivial, but what I am curious about is: - the 'explicit' appears to have been removed at version 1.35 (i.e. it was there at 1.34) and then re-introduced at 1.39. Is there some history to this? and - it looks like our code was falling into the second overload with 1.38 (the first overload was always explicit); with a fix it will now select the first overload, so for what case does the second overload now exist? --