On Mon, Jun 12, 2006 at 11:33:49PM +0200, Michael Walter wrote: > Maybe "switch" became a keyword with the patch.. > > Regards, > Michael >
That's correct. > On 6/12/06, M.-A. Lemburg <[EMAIL PROTECTED]> wrote: > > > > Could you upload your patch to SourceForge ? Then I could add > > it to the PEP. > > It's already up there :) I thought I sent that through in another e-mail, but maybe not: http://sourceforge.net/tracker/index.php?func=detail&aid=1504199&group_id=5470&atid=305470 Complete with documentation changes and a unit test. > > Thomas wrote a patch which implemented the switch statement > > using an opcode. The reason was probably that switch works > > a lot like e.g. the for-loop which also opens a new block. > > No, Skip explained this in an earlier e-mail: apparently some programming languages use a compile-time generated lookup table for switch statements rather than COMPARE_OP for each case. The restriction is, of course, that you're stuck with constants for each case statement. In a programming language like Python, where there are no named constants, the usefulness of such a construct might be questioned. Again, see Skip's earlier e-mails. > > Could you explain how your patch works ? > > 1. Evaluate the "switch" expression so that it's at the top of the stack 2. For each case clause: 2.1. Generate a DUP_TOP to duplicate the switch value for a comparison 2.2. Evaluate the "case" expression 2.3. COMPARE_OP(PyCmp_EQ) 2.4. Jump to the next case statement if false 2.5. Otherwise, POP_TOP and execute the suite for the case clause 2.6. Then jump to 3 3. POP_TOP to remove the evaluated switch expression from the stack As you can see from the above, my patch generates a COMPARE_OP for each case, so you can use expressions - not just constants - for cases. All of this is in the code found in Python/compile.c. Cheers, Tom -- Tom Lee http://www.vector-seven.com ----- End forwarded message ----- -- Tom Lee http://www.vector-seven.com _______________________________________________ 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
