Re: fall through switch/case in perl

[etcshadow]

Well, what the first couple folks said doesn't actually answer your question... they were answering what *would* have been your question if you *had* had break statements... I don't know if the original post was updated after the fact or if they simply did not actually read it... whatever.

The short answer is that there isn't anything that does this very well, and in the same way as C does. The thing to understand is that switch statements in C are actually just well-written GOTO statements! Likewise, the best way to do this might be GOTOs (as bad as that might sound)... or just coding it explicitly, something like:

for ( $var ) {
    my $go;
    ($go || $_ == 10) and $go++, print "a";
    ($go || $_ == 9 ) and $go++, print "b";
    ($go || $_ == 8 ) and $go++, print "c";
    ($go || $_ == 7 ) and $go++, print "d";
    ($go || $_ == 6 ) and $go++, print "e";
    ($go || $_ == 5 ) and $go++, print "f";
    ($go || $_ == 4 ) and $go++, print "g";
    ($go || $_ == 3 ) and $go++, print "h";
    ($go || $_ == 2 ) and $go++, print "i";
    ($go || $_ == 1 ) and $go++, print "j";
}

[TimToady]

Here's the computed goto version:

eval { goto 'L'.($var+0) }; die "$var out of range";
 
L10: print "a";
L9: print "b";
L8: print "c";
L7: print "d";
L6: print "e";
L5: print "f";
L4: print "g";
L3: print "h";
L2: print "i";
L1: print "j";
 
print "\n";

[Aristotle]

Shouldn't that be

eval { goto 'L'.($var+0) }; goto L_default;

L10: print "a";
L9: print "b";
L8: print "c";
L7: print "d";
L6: print "e";
L5: print "f";
L4: print "g";
L3: print "h";
L2: print "i";
L1: print "j";
L_default:

print "\n";

to preserve the semantics of the original code?

[BrowserUk]

The eval isn't required (unless I missed a subtlety?)

#! perl -sw
use strict;

my $var = 7;

goto 'CASE'.($var+0); die "$var out of range";

CASE10: print "a";
CASE9: print "b";
CASE8: print "c";
CASE7: print "d";
CASE6: print "e";
CASE5: print "f";
CASE4: print "g";
CASE3: print "h";
CASE2: print "i";
CASE1: print "j";

print "\n";

__END__
P:\test>junk
defghij

[etcshadow]

The eval is necessary if you want to fully emulate the C semantic of not dieing if there is no matching case. Really, the full-on computed goto method (I should have just written this into my top-level response) is this (I think):

{
eval { goto "CASE$var" } or goto DEFAULT;

    CASE10: print "a";
    CASE9:  print "b";
    CASE8:  print "c";
    CASE7:  print "d";
    CASE6:  print "e";
    CASE5:  print "f";
    CASE4:  print "g";
    CASE3:  print "h";
    CASE2:  print "i";
    CASE1:  print "j";
    DEFAULT: 
}

Which, admittedly, is not very different from Aristotle's. The only real difference being the outter braces. The purpose of them is to avoid polluting the label name-space. (Also, I prefer the "goto X or goto DEFAULT" over the "goto X; goto DEFAULT" purely for aesthetic reasons. :-D)

I sort of wonder why this isn't given as one of the ways of achieving C-like switch statement behavior in the perl docs? Oh, well... it's probably horribly inefficient or something (apart from just being too C-ish or something).