Re: [boost] [review] string convert

Subject: Re: [boost] [review] string convert
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2011-05-04 16:00:33

Vicente BOTET wrote:
> De : "Stewart, Robert"
> > Matthew Chambers wrote:
> > > On 5/4/2011 11:05 AM, Vicente BOTET wrote:
> > >
> > > > I agree that when a fail-back is given the user is not
> > > > interested in knowing if the conversion succeeded or not,
> > > > so in this case the return value should be T and not
> > > > optional T.
> > > > The question now is what function should be used,
> > > > convert_cast or try_convert_cast. As the function doesn't
> > > > throw I will use try_convert_cast, but as the function
> > > > returns type T I will use convert_cast.
> > >
> > > I disagree. I think the fallback with conversion success
> > > is a reasonable use case. Vladimir's case of notifying the
> > > user when a fallback value is being used is reasonable.
> > > It's difficult to leave that logic outside the conversion
> > > because only the conversion knows if and why the input is
> > > invalid.
> >
> > I agree with Matt.
>
> I don't see the added value then. If the user needs to check if
> the conversion succeeded, why not setting herself the fail-back
>
> int i;
> if (! try_convert_to(s,i))
> {
> i = fail_back;
> }

What are we comparing against?  I've lost track.  Shall we assume the default_value<T> customization point?

> > > string s = "4-2";
> > >
> > > // Matt likes to throw:
> > > int i = convert_cast(s);
> > >
> > > // Vladimir cares about success:
> > > int i = 17; if (!try_convert(s,i))
> > > { /* log that fallback value is being used */ }
> > >
> > > // except when he doesn't (but he never throws)
> > > int i = convert_cast(s, 17);
> > >
> > > // Vincente thinks success is optional:
> > > optional i = optional_convert(s);
> > >
> > > Note that in several of these, target typename is no longer
> > > needed, right?
> >
> > try_convert(s, i) doesn't tell me whether s is being
> converted to i's type or i to s's type.
>
> Is try_convert_to(s,i) better, or you see the same problem. Do
> you think it is better to use named parameters _from_ and _to?

It's try_convert_to<int>(s, i) which is better.  "_to<int>" makes it clear.

> > convert_cast(s, 17) has the same problem and breaks with the
> > new-style cast pattern.
>
> would you prefer to use a _failback named parameter?

s/failback/fallback/

My concern was that it needs to be convert_cast<int>(s, 17).

> If try_convert_to doesn't updates the target variable if
> conversion fails we can even write
>
> int i=17;
> try_convert_to(s,i);

I think that's the right semantic.

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


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