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Subject: Re: [boost] [review] string convert
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2011-05-03 14:26:08

Vicente BOTET wrote:

Vicente, you really need to try a different mail client or else use it differently. The angle brackets for your template parameter and argument lists are being dropped.

> In order to take care of types without default constructor I
> see several options:
> template
> Target convert_to(Source const& s, Target const& t);
> template
> Target& assign_to(Target& t, Source const& s);
> template
> struct default_value
> {
> T apply() { return T(); }
> };
> The user will need to specialize this function for types that
> are not default constructible.
> This meta-function will be used instead of declaring a
> defaulted variable in the string conversion function.
> T v(default_value::apply());

None of those options work for types without a default constructor *and* without a sentinel value.

> As a user I would prefer the second one

The name "assign_to" just seems odd to me. The problem is that assigning "123" to an int is the wrong idea. It isn't assignment but conversion. I understand you wanted a different name to account for the different behavior, but that's not it.

> In order to take care of no throwing semantics, I will choose
> to add a convert_to overloading with a error code parameter,
> not throwing without not knowing why fails seems too specific
> to me.
> template
> Target convert_to(Source const& s, err_code& ec);

That's fine if there are specific errors to report other than "bad input." The err_code type should also support a safe-bool conversion.

> But I could understand there are some cases where the single
> reason is a bad format. We could also use the no_throw_t as
> additional parameter, but in this case the return type should
> allow to know if the operation has succeed or not. If we follow
> the C++ standard interface the use of pair seems to be the more
> appropriated.
> template
> pair convert_to(Source const& s, no_thow_t const&);

This was already rejected by several folks. Allow me to add my dislike for it.

> Note also that there could be some conversions that could
> transport whether the conversion succeeds or not

I can't quite parse that.

> optional t = convert_to >(s);

Something important was lost in your message.

> or a Robert suggested overload the pointer to a source
> template
> optional convert_to(Source const* s);

Unfortunately, I realized that wouldn't work well for string literals, for example.

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

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