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This doesn't not intent to be nor became a standard. Instead it's thought to be a proof of concept for a construction which mimics switch/case statements. I think it's funny, so, i'll hope you enjoy it as I do.

Python, 59 lines
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from __future__ import with_statement
from contextlib import contextmanager

@contextmanager
def Switch():
    D = {}

    class _P(Exception): pass
    def _mkCase(var):
        class _PP(_P):
            V = var
            def __repr__(self):
                return str(self.V)
        D[var]=_PP
        return _PP
        
    def switch(var):
        if D.has_key(var):
            raise D[var]()
        raise _mkCase(var)()
    
    def case(var):
        if D.has_key(var):
            return D[var]
        return _mkCase(var)
    def default():
        return _P
        
    yield switch, case, default    
    

if __name__=="__main__":
    def test1():
        with Switch() as (switch, case, default):
            try: switch(55)
            except case(1):
                print 1
            except case(6):
                print 6
            except case(5):
                print 5
            except default():
                print 'default..'
    
    def test2():
        with Switch() as (switch, case, default):
            try:switch('hola')
            except case(1):
                print 1
            except case('holaS'):
                print 'holaS'
            except case('hola'):
                print 'hola'
            except default():
                print 'default..'
                
                
    test1()
    test2()

Discussion is open :-)

3 comments

Berthold Höllmann 14 years, 5 months ago  # | flag

Whats wrong with using dictionaries instead of Exceptions. Using exceptions to implement a switch syntax seems to be a misuse of exceptions to me. I always thought dictionaries are the way to go:

switch = {1: 1,
          6: 6,
          5: 5}
print switch.get(55, 'default..')

switch = {1: 1,
          'holaS': 'holaS',
          'hola': 'hola'}
print switch.get('hola', 'default..')
David Weil (author) 14 years, 5 months ago  # | flag

Whats wrong with using dictionaries instead of Exceptions. There's nothing wrong.

That's the way to do kind-of switch, other way is to have something polymorphic.

I've made as an exercise.

Mike McGowan 14 years, 4 months ago  # | flag

Functions! I've found that functions are typically replaced with a None in a dictionary. This seems to be the only way to get around it.

Created by David Weil on Sun, 17 Jun 2007 (PSF)
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