On 6/19/06, Raymond Hettinger <[EMAIL PROTECTED]> wrote: > Guido van Rossum wrote: > On 6/18/06, Josiah Carlson <[EMAIL PROTECTED]> wrote: > > [...] Offering arbitrary expressions whose > meaning can vary at runtime would kill any potential speedup (the > ultimate purpose for having a switch statement), [...] > > Um, is this dogma? Wouldn't a switch statement also be a welcome > addition to the readability? I haven't had the time to follow this > thread (still catching up on my Google 50%) but I'm not sure I agree > with the idea that a switch should only exist for speedup. > > A switch-statement offers only a modest readability improvement over > if-elif chains.
Probably, which is why it hasn't been added yet. :-) But there is a definite readability improvement in that you *know* that it's always the same variable that is being compared and that no other conditions are snuck into some branches. > If a proposal introduces a switch-statement but doesn't > support fast dispatch, then it loses much of its appeal. Historically, the > switch-statement discussions centered around fast dispatch without function > call overhead or loss of direct read/write to local variables (see > sre_compile.py and sre_parse.py for code would would see a speed benefit but > almost no improvement in readability). Well yes duh, of course a switch syntax should be as fast as a corresponding if/elif dispatch series. (I look upon dict-of-functions-based dispatch as a tool for a completely different use case.) Perhaps I misunderstood Josiah's comment; I thought he was implying that a switch should be significantly *faster* than if/elif, and was arguing against features that would jeopardize that speedup. I would think that it would be fine if some switches could be compiled into some kind of lookup table while others would just be translated into a series of if/elifs. As long as the compiler can tell the difference. -- --Guido van Rossum (home page: http://www.python.org/~guido/) _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
