Re: [boost] Boost review of the Convert library is ongoing

Subject: Re: [boost] Boost review of the Convert library is ongoing
From: Krzysztof Czainski (1czajnik_at_[hidden])
Date: 2014-05-23 02:44:44

2014-05-23 2:25 GMT+02:00 Vladimir Batov <Vladimir.Batov_at_[hidden]>:
[...]

template<class TypeOut, class TypeIn>
> boost::optional<TypeOut> operator()(TypeIn const&); //#3
>
> surely seems attractive and with that interface converters can be easily
> used on their own (if needed/preferred) bypassing "convert" api altogether.
>
> Let's take a simple case of, say, the "direction" class from the docs
> (which has no default constructor) and try converting it to std::string.
> Say, we want that conversion possible using a few converters with
> std::sstream-based being one of them. In that setting I say #1 has the
> following advantages (no matter how ugly I personally find it):

[...]

> template<TypeIn, TypeOut>
>
 boost::optional<TypeOut>
> basic_stringstream_converter::operator()(const TypeIn& in)
> {
>     boost::optional<TypeOut> out = boost::make_optional(boost::
> convert_default_maker<TypeOut>::make());
>
>     stream_.str(std::basic_string< char_type>());
>     stream_ << in; stream_ >> *out;
>
>     return out = stream_.fail() ? boost::optional<TypeOut> : out;
> }
>
> template<TypeIn, TypeOut>
> boost::optional<TypeOut>
> lexical_cast_converter::operator()(const TypeIn& in)
> {
>
>     try
>     {
>         boost::optional<TypeOut> out_value = boost::make_optional(boost::
> convert_default_maker<TypeOut>::make());
>         *out_value = boost::lexical_cast<TypeOut>(in);
>         return out;
>     }
>     catch (...)
>     {
>         return out = boost::optional<TypeOut>;
>     }
> }
>

Why would you make a default TypeOut to then assign to it, instead of:

template<TypeIn, TypeOut>
boost::optional<TypeOut>
lexical_cast_converter::operator()(const TypeIn& in)
{

    try
    {
        return boost::lexical_cast<TypeOut>(in);
    }
    catch (...)
    {
        return boost::none;
    }
}

Regards,
Kris