Re: [boost] Formal Review Request: Boost.Convert

Subject: Re: [boost] Formal Review Request: Boost.Convert
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-02-23 11:13:31

On Sunday, February 22, 2009 11:31 PM
Vladimir Batov wrote:
>
> Now I understand that Boost.Parameter allows me to call
>
> convert<string, int>(str, some_user_defined_param = ...);
>
> As I understand Boost.Convert does not know and does not make use of
> "some_user_defined_param" but takes it in using ArgumentPack.
> How then does
> the parameter make it to some user-defined formatter? Maybe
> it is because I
> am still thinking in terms of manipulators -- a user writes
> his own and
> plugs it into Boost.Convert as
>
> convert_to<int>(str) >> std::hex;
>
> How do we do that with Boost.Parameter? Should we
> write/specify some kind of
> Boost.Parameter-aware manipulator? What the signature then
> might be? Is
> there some other way?

std::hex assumes some state in the stream for storing that hexadecimal formatting should be used in a subsequent conversion step.  IOStreams provides a means to tack on extra state not built in (iword(), pword(), and xalloc()), so that's how user-defined formatting could save state to be used later, but it still requires the cooperation of the manipulators to set the state and the formatting logic invoked later.

That same, save state and use it later when converting is needed for something like convert.

>     convert<string, int>(str, default_ = -1, throw_ = false);
>
> indeed looks trendy and I probably could extend the convert()
> interface that
> far. However, I understand Andrey's interest is in the user
> providing his
> own keyword (like throw_on_out_of_range_) so that it could be
> used somewhere
> for formatting. Where and how that's what I am having
> difficulty with (due
> to no experience with Boost.Parameter).

I'd still like to see a coherent set of requirements.  There are too many forces tugging on the concept from what appear to be competing directions.

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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