Re: [boost] Re: [optional]output

From: Peter Dimov (pdimov_at_[hidden])
Date: 2005-03-09 11:03:59

David Abrahams wrote:
> "Peter Dimov" <pdimov_at_[hidden]> writes:
>
>> David Abrahams wrote:
>>> If you want to be unambiguous, it has to be more like:
>>>
>>>     [hello] <- a non-empty optional<std::string>
>>>     []      <- a non-empty optional<std::string> (the string is
>>>     empty) _       <- an empty optional<T>
>>
>> My preference is
>>
>>    hello
>>
>>    _
>>
>> A string can never be output "correctly", no matter what the
>> delimiters are ("a] [b").
>
> I disagree.  You can generate escapes:
>
> [a\] \[b]
>
> or if you like,
>
> [a\]\ \[b]

I should have been more clear. You shouldn't attempt to fix the output of a 
std::string in optional<>'s operator<<. The proper way to make a std::string 
bi-directional is by defining appropriate operator<< and operator>> 
overloads for std::string. As these operators are already defined and are 
not bi-directional in the general case, optional<std::string> should not 
attempt to provide extra bi-directionality.

I would concentrate on making simple bi-directional types working correctly, 
and outputting a placeholder token such as _ for an empty optional is one 
way to accomplish this that produces a reasonably clear output (although it 
requires a putback, which is sadly not guaranteed to work).