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Subject: Re: [boost] Review Request: Introduction of boost::string namespace and string-conversion functions
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-02-11 15:05:39

From: boost-bounces_at_[hidden]
[mailto:boost-bounces_at_[hidden]] On Behalf Of

> I would like to propose to create a new
> boost::string
> namespace where I'd expect all string-related functionality might be
> logically housed.

Sounds right.

> >From the user point the interface I'd like to propose might
> look like the
> following:
> int i;
> std::string s;
> 1) int i_from_s = boost::string::to<int>(s); // throws
> 2) std::string s_from_i = boost::string::from<int>(i);
> 3) bool s_is_i = boost::string::is<int>(i);

"is" is a poor name choice. It doesn't imply "can convert to." What's more, in order to arrive at the answer, I imagine one must actually try the conversion, so it would be better to provide a conversion function that returns false rather than throwing an exception on failure:

  if (boost::string::from<int>(s, i))


  if (boost::string::to<int>(i, s))

(I always put mutable parameters first in my code, but I can see an argument that they should follow the order of the types in the qualified call: string::to<int>(s, i).)

> 4) int i_from_s = boost::string::to<int>(s)(-1);
> The above is a non-throwing variation of #1 with the default value
> provided for failed conversion.

That would read better as:

   int j(boost::string::to<int>(s).or(-1));

> 5) int i_from_s = boost::string::to<int>(s)(std::hex);
> 6) std::string s_from_i = boost::string::from<int>(i)(std::hex);
> The above is variations of #1 and #2 with the std::hex
> manipulator/formatter applied.

This is interesting, but I don't like the new syntax relative to IOStreams. How about this:

   int l(boost::string::to<int>(s) >> std::hex);

This implies a stream in the object returned from to<int>(s) on which the manipulator can be applied.

> 7) int i_from_s =
> boost::string::to<int>(s)(-1)(std::hex)(yet-another-manipulator);

That looks odd.

> Off the cuff the actual conversion might look something along the
> following lines:
> template<class T, class Char>
> boost::string::value::operator T()
> {
> std::basic_istringstream<Char> stream(string_);
> if (manipulators) stream >> manipulator_ >> ... >> value_;
> else stream >> value_;

   if (manipulators) stream >> manipulator1 >> ...;
   stream >> value_;

> if (
> if (no_default) throw something;
> else return default_value_;
> return value_;

That could be managed in derived value types based upon the signature of the calling function rather than using data members and conditional logic to react.

Rob Stewart robert.stewart_at_[hidden]
Software Engineer, Core Software using std::disclaimer;
Susquehanna International Group, LLP

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