> This switch statement RFC seems to be built on the premise that the
> reason to have a switch statement is to remove a common parameter
> from the following limited form conditional expressions.
Yes. As I point out in the paper, that's the *nature* of a switch statement.
To distribute a test spatially, by factoring.
> However, while the table of 16 different ways in which two values
> could generate a match is interesting, it can only ever perform at
> most two operations per pair of types (depending on which type is
> found in which of the two positions).
Not so:
switch ($value) {
case 1 {...} # numeric equality
case "a" {...} # string equality
case $obj {...} # referential equality
case /pat/ {...} # pattern match
case %hash {...} # hash lookup
case [1..10] {...} # list inclusion
case __<100 {...} # subroutine return
}
Granted one would rarely want all these at once, but a non-trivial subset
is entirely plausible:
sub classify {
switch ($_[0]) {
case 0 { return 'zero' }
case \&odd { return 'odd' }
case [1..9] { return 'even' }
case /[a-f]/i { return 'hex' }
}
}
> I find it unlikely that the casual Perl programmer, and even many
> expert Perl programmers, will be able to usefully memorize the list
> of operations proposed for the type pairs. This inability to
> memorize the list will no doubt curl the corner of the switch page
> in the perl documentation.
No. The whole point is that they just DWIM.
> I think the fundamental purpose of the switch statement is to
> choose one (generally) of many cases, and that the factoring of one
> of the parameters is what gets in the way of having a rich set of
> matching operations.
Just selecting one from many alternatives is a cascaded if's job.
The defining characteristic of a switch the the factoring of some part
of the comparisons. And it's an important characteristic, because it
focussed the reader's mind on the commonality of the test.
> Hence, I think it suffices to have a single keyword for switch: not
> "switch", but "case". The block containing "case" would be the
> switch statement. "case" is simply a rename of "elsif" whose first
> occurrence in a block simply pretends to follow "if (0) {}".
If that's the consensus, let's just have elsif.
But I don't think that's the consensus.
I appreciate your comments, but I certainly intend to push ahead with
the proposed syntax -- as I proposed it. A very large number of people
like it as it is. If I'm wrong, let Larry kill it.
Damian
