Re: [boost] Formal Review Request: Boost.Convert

Subject: Re: [boost] Formal Review Request: Boost.Convert
From: Vladimir Batov (batov_at_[hidden])
Date: 2009-02-22 05:04:50

>> I looked a Boost.Parameter and will certainly try using it somewhere. My 
>> hesitation with it for boost::convert is I am under impression that the 
>> set of acceptable parameters (radix_, etc.) has to be predefined and 
>> therefore cannot be extended by the user when formatting like 
>> "convert(str) >> std::hex" seems more flexible.
>
> You can add new keywords as needed.

Where can I add those "new keywords" to? If it is into convert(),  then I do 
not feel it is appropriate as for every user "needed" will be different and 
I cannot see convert() collecting *all* those "needed" keywords from every 
user on the globe.

> The point is that the underlying conversion mechanism can support a subset 
> of these keywords, specific to the conversion domain. This way it will be 
> a non-intrusive extension.

I cannot understand how it can be a "non-intrusive extension" if every new 
keyword needs to be stored/registered *inside* convert<string, int>... 
unless I misunderstand something. With manipulators (however clumsy they 
are) convert<string, int> knows nothing about std::hex. Still, when std::hex 
is plugged in, we get 0xFF. How do you do that with "radix_"? The keyword 
has to be registeded with convert<string, int> and then convert<> needs to 
apply that somehow.

Secondly, I do not feel there is much conceptual difference between

    convert<string, int>(str, radix_ = 16)
and
    convert<string, int>(str).radix(16) // 16 passed in differently
or
    convert<string, int>(str) >> radix(16) // different op>>
or
    convert<string, int>(str) >> std::hex

The difference is that in #1 convert() has to handle "radix_" itself and in 
#4 convert() knows nothing about std::hex. Am I missing something?

RE: algorithms

I've extended convert to be used with algorithms as

std::vector<string> strings;
std::vector<int> integers;
...
std::transform(
    strings.begin(),
    strings.end(),
    std::back_inserter(integers),
    convert<string, int>(string(), -1));

No formatting. I feel it is the best I can do (well, so far).

> convert<string, short >(0xFFFFFFFF, throw_on_out_of_range_ = true)?

Looks certainly tempting. However, I do not believe it is achievable. For 
that to happen every parameter (like throw_on_out_of_range_) needs to be 
integrated into, say, convert<string, int> and then its value stored to be 
re-applied for every entry during traversal. Far too expensive. 
convert<string, type> has already grown beyond anything I ever imagined. I 
might well not understand what you are advocating. Can you put together some 
kind of proof-of-concept code for me to better understand how you want to do 
that.

V.