range stuff

[Andrei Alexandrescu]

Michel Fortin wrote:
> On 2009-02-16 20:21:00 -0500, superdan <super at dan.org> said:
> 
>> a'ight i've read all range stuff n ruminated on it for a while. yer 
>> ranges suck goat balls. something's amiss.
>>
>> yer have ranges that generate stuff.  some even ferever. then yer have 
>> ranges that eat stuff output ranges that is. but there's no range that 
>> has both input and output. some sort of filter ranges. yer should 
>> connect stuff together to get chains n stuff. see? i'm sayin': why 
>> would ya have a piehole & an asshole if yer don't have a stomach.
>>
>> i/o ranges are a missing link. if yer smart u can unify range stuff 
>> and stream stuff together. then stream or range it's all the same. not 
>> sure its possible but if it is only yer can pull it. that would be 
>> dogs bollocks.
> 
> Interesting. In fact I started a prototype of some kind of filter range 
> for tokenizing XML: takes characters and gives tokens. That said, what 
> you get is an input range (you can read tokens) that you build from an 
> other input range (character range). So while it may fit the definition 
> of a filter range, it may not be what you're thinking about.
> 
> What you want, an output range linked to an input range makes me think 
> of the XmlEventReaderToWriter class in BerkelyDB XML, although in 
> reverse (writer to reader) since ranges aren't pushing events, but 
> pulling data when requested.
> <http://www.oracle.com/technology/documentation/berkeley-db/xml/api_cxx/frame.html> 
> 
> 

I think filtering ranges are a great idea. Some were already present 
without a formal interface, e.g. map has an input and an output. All I 
need is to define a common interface for connecting a range to another. 
To that end, I will proclaim that if a range has the primitive

setInput(SomeRange input)

then it is a filtering range. This will be very useful for e.g. 
transcoding (we'll need at some point to rewrite std.encoding): a 
newly-defined character type SomeChar must define a filtering range that 
eats ranges of SomeChar and outputs dchar, and also a filtering range 
that eats dchar and produces SomeChar. Then that filter can be used to 
transfer characters across strings but also any combination of ranges 
including files.


Andrei