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Subject: Re: [boost] [convert] Version in the Vault ready for review.
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-03-24 10:36:38

On Sunday, March 01, 2009 7:02 PM
Vladimir.Batov_at_[hidden] wrote:
> it will be very useful to many developers (like me) not
> satisfied with
> lexical_cast and not (yet?) needing (or ready for) something
> like upcoming
> Spirit 2.0.

It does seem as if the middle ground would be useful.

> The current interface can be summed up as with as little as
> int i = convert<int>::from(str); // Throws on failure
> int i = convert<int>::from(str, -1); // Returns -1 on failure
> More details can be found in the accompanying document (just
> remember I am
> not Shakespeare).

There's room to improve the document, of course, but it is a very nice start. The result type's documentation is rather hidden, unfortunately, as it appears in the "Conversion-Failure Check" section. It should be prominently featured in one of the early sections.

I wonder about making the result returning interface explicit. That is, change the two interfaces shown above to return TypeOut and add a new call, something like the following, that returns a result instance:

   convert<int>::result result(convert<int>::try_from(str));

That eliminates all conversion, template deduction, and temporary object overhead issues for the first two calls. It also makes explicit when there's a result object.

I think the result type's conversion functions should throw an exception if !good(). Then, there's no need for your dothrow:

   convert<direction>::result result(convert<direction>::try_from(str, up_dir));
   direction dir(result); // throws exception if !result.good()

I dislike the nothrow idea since it implicitly provides a default of TypeOut() and there's already an interface for specifying a default. I'd rather folks wrote this:

   int i(convert<int>::from("not an int", 0));

than this:

   int i(convert<int>::from("not an int") >> boost::nothrow);

Your locale example fails to break a line:

   std::locale...// Windows-style locale d1 = convert...

which should be:

   std::locale new_locale(...); // Windows-style locale
   string d1 = convert<string>::from(d)

I have some issues with the implementation, but I'll defer to another time.

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

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