>went through the archives about RFC22 "builtin switch statement".
>didn't see any mention of this, thought I'd throw it in there to see
>how it was recieved.
>I was thinking that the switch statement could possibly be expanded
>to also behave as an operator and not just a control statement.
>i.e. the way the trinary conditional operator works:
>my $final = $boolean ? $this_value_if_true : $else_this_value;
>except you could do a case operator:
>my $final = switch ( $val ) {
> case 0 { $zero_val;}
> case 1 { $one_val;}
> case 2 { $two_val;}
> case 3 { $three_val;}
> };
>From Camel 3:
Cascading use of the C<?:> operator can also work for simple
cases. Here we use again a C<for> for its aliasing property
to make repeated comparisons more legible:
for ($user_color_preference) {
$value = /red/ ? 0xFF0000 :
/green/ ? 0x00FF00 :
/blue/ ? 0x0000FF :
0x000000 ; # black if all fail
}
For situations like this last one, it's sometimes better to build
yourself a hash and quickly index into it to pull the answer out.
Unlike the cascading conditionals we just looked at, this one
scales to an unlimited number of entries, and takes no more time
to look up the first one than the last. The disadvantage is that
you can only do an exact lookup, not a pattern match. If you
have a hash like this:
%color_map = (
azure => 0xF0FFFF,
chartreuse => 0x7FFF00,
lavender => 0xE6E6FA,
magenta => 0xFF00FF,
turquoise => 0x40E0D0,
);
Then exact string lookups run quickly:
$value = $color_map{ lc $user_color_preference } || 0x000000;
Even complicated multi-way branching statements (with each case
involving the execution of several different statements) can be
turned into fast lookups. You just need to use a hash of references
to functions. See L<Chapter ##, References> for how to handle
those.
I've actually even used this at run-time, such as:
$value = {
azure => 0xF0FFFF,
chartreuse => 0x7FFF00,
lavender => 0xE6E6FA,
magenta => 0xFF00FF,
turquoise => 0x40E0D0,
}->{ lc $user_color_preference } || 0x000000;
I did that because it was more legible and more convenient although
I confess that that's "rather" inefficient compared with a table
that's built only once. (Convenience and legibility tend to place
higher on my priority list than "efficiency", since convenience ==
human-efficiency. :-)
Now, some built-in syntax thingie would be even more efficient,
since it could all be done at compile time. I'd have to go read
Damian's switchy paper; I'd be surprised if this weren't there.
--tom
