[Python-Dev] Switch statement (original) (raw)

Phillip J. Eby pje at telecommunity.com
Sat Jun 24 19🔞23 CEST 2006

At 07:04 PM 6/24/2006 +0200, Fredrik Lundh wrote:

I don't see this as much of a problem, really: we can simply restrict the optimization to well-known data types ("homogenous" switches using integers or strings should cover 99.9% of all practical cases), and then add an opcode that checks uses a separate dispatch object to check if fast dispatch is possible, and place that before an ordinary if/elif sequence.

What about switches on types? Things like XML-RPC and JSON want to be able to have a fast switch on an object's type and fall back to slower tests only for non-common cases. For that matter, you can build an effective multiway isinstance() check using something like:

 for t in obtype.__mro__:
     switch t:
     case int: ...; break
     case str: ...; break
     else:
         continue
 else:
     # not a recognized type

This is essentially what RuleDispatch does in generic functions' dispatch trees now, albeit without the benefit of a "switch" statement or opcode.

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