Re: [boost] Boost Units library preview

From: Jeff Garland (jeff_at_[hidden])
Date: 2006-08-29 16:24:02

Ben Strasser wrote:
> Jeff Garland <jeff <at> crystalclearsoftware.com> writes:
> 
>>> typedef unit<length, "m"> meter;
>> This isn't valid code...can't give char strings to templates.
> I was talking about an ideal world. ;)

Ok, well we don't have that world...

>> The problem is hardcoding the "m" anywhere -- this shouldn't be done.  You 
>> need an I/O facet that has the defaults and can be overridden by the user at 
>> runtime.  This allows different output for the same value in the same process. 
>>   Your view of how to solve this is on the wrong course in my view...
> 
> I depends on the situation. Some units are unique to the application. Here we
> probably wont need any internationalization so hard coding "m" will do the job
> just fine.

Boost is an international organization with an international audience so it's 
a different context to do something only for yourself.

> There are however also other units. For example length units. It might be useful
> to let the programmer use meters in his program and have it output feet based on
> the local in the stream.
> 
> What I mean is something like:
> 
> cout.imbue(new unit_out_facet<length, feet>("", "ft"));
> wcout.imbue(new unit_wout_facet<length, feet>(L"", L"ft"));
> //or
> cout.imbue(new unit_out_facet<length, meter>("", "m"));
> wcout.imbue(new unit_wout_facet<length, meter>(L"", L"m"));
> //...
> cout<<meter(4); // will print meter or feet based on the current local
> 
> This seems as a good idea to me and this is possbile to implement.

On the right track, but this scares me a bit.  I'm not sure I want conversions 
in the facet code.  I think I'd rather the user do that explicitly.

> Input would be a bit more tricky.

Input is much harder...because you only have access to an input iterator.  You 
can't backtrack.  So suppose you want to handle input like this:
   10 m
   10 meters
   10 microseconds

The first 2 are a valid length -- the last isn't.  Anyway, it's sticky.

>> Don't take this as criticism -- I suppose I could have taken this on by now 
>> given my experience.  I'm just hoping someone will take up my challenge 
> No, I don't. I like hearing other peoples opinions.

Good :-)

Jeff