RE: [boost] lexical_cast reviewed
-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org]On Behalf Of Jason Sent: vrijdag 16 juli 2004 11:03 To: boost@lists.boost.org Subject: [boost] lexical_cast reviewed
SOURCE CODE: #include <sstream> using namespace std;
class lexical_cast { public: template <typename Source> lexical_cast( const Source & source ) { ss << source; }
template <typename Target> operator Target() { Target target; ss >> target; return target; } private: stringstream ss; };
Not really lexical_cast, but useful nevertheless. Perhaps we could call it lexical_auto_cast. It could be more efficient to store a string instead, but I'm not sure. Regards, Michiel Salters This e-mail and any attachment is for authorised use by the intended recipient(s) only. It may contain proprietary material, confidential information and/or be subject to legal privilege. It should not be copied, disclosed to, retained or used by, any other party. If you are not an intended recipient then please promptly delete this e-mail and any attachment and all copies and inform the sender. Thank you.
On Fri, Jul 16, 2004 at 03:06:20PM +0200, Michiel Salters wrote:
-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org]On Behalf Of Jason Sent: vrijdag 16 juli 2004 11:03 To: boost@lists.boost.org Subject: [boost] lexical_cast reviewed
SOURCE CODE: #include <sstream> using namespace std;
class lexical_cast { public: template <typename Source> lexical_cast( const Source & source ) { ss << source; }
template <typename Target> operator Target() { Target target; ss >> target; return target; } private: stringstream ss; };
Not really lexical_cast, but useful nevertheless. Perhaps we could call it lexical_auto_cast. It could be more efficient to store a string instead, but
I'm not sure.
That would mean the lexical_cast ctor constructs a string member, constructs a local stringstream, inserts Source into the stream, assigns to the string, then destroys the local stringstream. Then when the conversion takes place another local stringstream is created, copying the contents of the string, then Target extracted, then the stringstream is destroyed. In the dtor the string member is destroyed. This is an extra std::string ctor/dtor and an extra std::stringstream ctor/dtor over the original, and at least one copy of the string data, maybe more (depending on how the string is implemented). As for the original suggestion - I like the fact that lexical_cast<T>() is consistent with the syntax of const_cast<T>(), static_cast<T> etc. so I don't think the name should include "cast" unless it matches that syntax. There should also be error-checking in the conversion operator, to check that the stream state is good before (in case insertion failed) and after extracting. Can't check in ctor since the Target type isn't known yet. (Obvious I know - just thinking out loud ... ) Also, I think Jason's version would fail in this case, that the original supports: struct A { A(const B&); }; struct B {}; struct C {}; std::ostream& operator<<(std::ostream&, const C&); std::istream& operator>>(std::istream&, const B&); A a = boost::lexical_cast<B>( C() ); // OK A a = lexical_cast( C() ); // ERROR, no op>> for A Similarly if B has "B::operator A() const" instead of A having non-explicit "A::A(const B&)" ctor. I'm not sure how important this is, since it should be possible to construct pathological cases that the original version fails with too. jon -- "It is easier to port a shell than a shell script." - Larry Wall
participants (2)
-
Jonathan Wakely -
Michiel Salters