[Python-Dev] PEP 246: lossless and stateless

[Clark C. Evans]

On Fri, Jan 14, 2005 at 09:47:15AM +0000, Armin Rigo wrote:
| In my opinion a user-defined class or interface mixes two notions: a
| "concept" meaningful for the programmer that the instances
| represent, and the "interface" provided to manipulate it.
...
| This suggests that only concrete objects which are expected to
| encode a *single* concept should be used for adaptation.

So, in this view of the world, the adapter from FileName to File _is_ 
appropriate, but the adapter from String to FileName isn't?

  def checkSecurity(filename: FileName):
      ...
 
Hmm.  I'd like to be able to pass in a String here, and use that
String->FileName adapter.  So, there isn't a problem yet; although
String is vague in a sense, it doesn't hurt to specialize it 
in the context that I have in mind.

   def checkContent(file: File):
       ... look for well known viruses ...

   def checkSecurity(filename: FileName):
       ... look for nasty path information ...
       return checkContent(filename)
       
Even this is _ok_ since the conceptual jump is specified by the
programmer between the two stages.  The problem happens when
one does...

    checkContent("is-this-a-filename-or-is-this-content")
    
This is where we run into issues.  When an adapter which 'specializes'
the content is used implicitly in a trasitive adaption chain.

| Note that it may be useful to be able to register some adapaters 
| in "local"  registeries instead of the single global one, to avoid 
| all kinds of unexpected global effects.

Nice...

Best,

Clark

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Clark C. Evans                      Prometheus Research, LLC.
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