OT: Re: Just took a look in the perl newsgroup....

[Cliff Wells]

On Thu, 2003-05-29 at 10:40, Carl Banks wrote:
> Better, perhaps, have the "case" cache results, like this:
> 
>     _case_cache = {}
> 
>     def case(v):
>         if _case_cache.has_key(v):
>             return _case_cache[v]
>         class Case(Exception):
>             value = v
>         _case_cache[v] = Case
>         return Case
> 
>     switch = case
> 
> 
> Then the resulting case statement looks like:
> 
>     try: raise switch(n)
>     except case(1):
>         print 1
>     except case(2):
>         print 2
>     except:
>         print 'default'

This thread has been most intriguing.  I doubt I would ever use this
stuff in 'real' code, but still, fun to play with.  Here's my version of
the above:

class _switch:
    def __call__(self, v):
        class Case(Exception): value = v
        self._value = Case
        raise self._value

    def case(self, v):
        if not hasattr(self, '_value'):
            raise # raise "real" exceptions in user code

        if self._value.value == v:
            return self._value
        return v
    
    def default(self):
         return self._value
    
switch = _switch()
case = switch.case
default = switch.default

for v in range(1,6):
    print v,
    try: switch(v)
    except case(1):
        print 1
    except case(2):
        print 2
    except case(4):
        print 4
    except case(v):
        print "one way to spell default"
    # except default():
    #    print "another way to spell default"


This has a couple of advantages:
1.  Doesn't stomp all exceptions, i.e. switch(x) in the above code would
still raise NameError (although there might be a better way of doing
this, I just got tired of tinkering with it).
2.  Doesn't have a global cache.
3.  Doesn't require 'raise switch()' which I found unacceptable <wink>

Still, given the nature of the problem, it's still probably wrong in one
way or another.

> Very neat, clever idea.

Indeed.

-- 
Cliff Wells, Software Engineer
Logiplex Corporation (www.logiplex.net)
(503) 978-6726  (800) 735-0555