[boost] Re: [optional]output

From: Fernando Cacciola (fernando_cacciola_at_[hidden])
Date: 2005-03-09 14:51:29

"David Abrahams" <dave_at_[hidden]> escribió en el mensaje 
news:uwtsgbzti.fsf_at_boost-consulting.com...
> "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]
>
>
Well, I hope that by now it is obvious why I didn't add this operator to 
begin with.
Since it can always be added externally in the context of the client code, I 
simply decided to let her/him do that, using whatever format suits in that 
context.
But I suppose I could provide *some* IO even if imperfect.

I see 2 distinct purposes for operator <<
One is to provide a readable output, the other some form of serialization.
Given that we have the serialization library, I believe it is (or has to be) 
its job to provide a suitable encoding scheme to fully "textualize" and 
"parse" an optional<T>. Specially since to parse it back you may also need 
to encode the type.

If I would only focus on providing a readable output, I would take Peter's 
suggestion and simply use "_" or some such as a textual empty optional<>. 
However, this totally breaks any chance to parse it.

Ryan's suggestion supports parsing, and so does Joel's, which is much 
terser, so I like it better.
But I agree with David that his suggested format is even less ambiguous.

Therefore, so far, I'm taking Joel's + David's proposal:

It supports some form of simple parsing (if you know the type) and provides 
a somewhat readable output as well.

[<text>]

  A non-empty optional<T> with value: lexical_cast<T>(<text>)
  <text> can be an empty string

_

 An empty optional<T>

Best,

Fernando Cacciola