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IWETHEY Home / IWETHEY Board / Theory and Practice of Programming Forum / Is this a sort of typecasting?
Post #178,301
by tuberculosis
Picture of tuberculosis
10/7/04 5:36:33 PM
Reply
New Is this a sort of typecasting?
push @{ $norm{$val} }, $key;

Specifically the @{ }

I ask because later on when trying to print out the list I end up needing to say

for my $item ( @{ $norm{$key} } ) { print $item; }

where I had to add the @{ } to get something different from <ARRAY0xCRAP> from printing and see the elements again.

I expected $norm{$key} to be a list but it seems to be more like some kind of wrapper.


That was lovely cheese.

     --Wallace, The Wrong Trousers
Post #178,311
by Simon_Jester
10/7/04 6:00:50 PM
Reply
New It's a reference
Post #178,312
by ben_tilly
10/7/04 6:10:14 PM
Reply
New Sort of
What's actually happening is that $norm{$val} is the reference to the array. Decorating it by @{ $norm{$val} } accesses the array.

It's the same kind of dereferencing that you go through in C to get at a struct that you have a pointer to.

You could also write ${ $norm{$val} }[3] to access the 4'th element. Or use the syntactic shortcut $norm{$val}[3].

As for your expectation, you're tripping over the fact that Perl is a list-oriented language. There is no such thing as a straight list in Perl. Nothing will act "like a list". Instead in a lot of places things will be interpreted as lists and will do something interesting.

Cheers,
Ben
I have come to believe that idealism without discipline is a quick road to disaster, while discipline without idealism is pointless. -- Aaron Ward (my brother)
     Perl frustrations - (tuberculosis) - (45) - Oct. 7, 2004, 03:55:53 PM EDT
         Simple solution - (ben_tilly) - (10) - Oct. 7, 2004, 05:31:13 PM EDT
             Bleh. - (admin) - (3) - Oct. 7, 2004, 04:42:49 PM EDT
                 That's because you approached it wrong - (ben_tilly) - (2) - Oct. 7, 2004, 05:22:57 PM EDT
                     I'm gradually warming up to it - (deSitter) - Oct. 7, 2004, 09:08:18 PM EDT
                     That should be in the man page. - (static) - Oct. 8, 2004, 02:17:42 AM EDT
             Is this a sort of typecasting? - (tuberculosis) - (2) - Oct. 7, 2004, 05:36:33 PM EDT
                 It's a reference -NT - (Simon_Jester) - Oct. 7, 2004, 06:00:50 PM EDT
                 Sort of - (ben_tilly) - Oct. 7, 2004, 06:10:14 PM EDT
             Interesting.... - (Simon_Jester) - (2) - Oct. 7, 2004, 05:58:41 PM EDT
                 The solution would have its own problems - (ben_tilly) - (1) - Oct. 7, 2004, 06:27:50 PM EDT
                     <bow> thank you. -NT - (Simon_Jester) - Oct. 7, 2004, 11:14:47 PM EDT
         THank you for stepping on this rake - (Arkadiy) - (33) - Oct. 7, 2004, 05:20:48 PM EDT
             He was overcomplicating it - (ben_tilly) - (32) - Oct. 7, 2004, 05:30:04 PM EDT
                 Well, maybe - (tuberculosis) - (17) - Oct. 7, 2004, 05:43:24 PM EDT
                     Agreed - (ben_tilly) - (16) - Oct. 7, 2004, 06:12:17 PM EDT
                         Agree its a mistake - (tuberculosis) - (15) - Oct. 7, 2004, 06:36:09 PM EDT
                             Same here. - (admin) - Oct. 7, 2004, 06:45:32 PM EDT
                             Right - (ben_tilly) - Oct. 7, 2004, 06:56:48 PM EDT
                             Shame about the inertia. Python's design is "least surprise" - (FuManChu) - (12) - Oct. 7, 2004, 10:02:43 PM EDT
                                 When I started with Perl... - (ben_tilly) - (11) - Oct. 7, 2004, 10:53:12 PM EDT
                                     On Perl 6 - (pwhysall) - (3) - Oct. 8, 2004, 01:53:55 AM EDT
                                         Re: On Perl 6 - (Yendor) - Oct. 8, 2004, 08:37:56 AM EDT
                                         I had a nice response to this typed up - (ben_tilly) - (1) - Oct. 8, 2004, 12:54:37 PM EDT
                                             Many thanks for that - (pwhysall) - Oct. 9, 2004, 02:53:04 AM EDT
                                     We're having a little brown bag on Ruby - (tuberculosis) - (4) - Oct. 8, 2004, 12:46:50 PM EDT
                                         Re: We're having a little brown bag on Ruby - (JimWeirich) - (3) - Oct. 11, 2004, 06:55:34 AM EDT
                                             Shhh! Anonymous Todd works at some other... - (CRConrad) - Oct. 11, 2004, 07:36:30 AM EDT
                                             I might have been there - (tuberculosis) - (1) - Oct. 11, 2004, 12:55:46 PM EDT
                                                 Re: I might have been there - (JimWeirich) - Oct. 11, 2004, 01:14:57 PM EDT
                                     Re: strict -- have you seen pychecker? - (FuManChu) - (1) - Oct. 8, 2004, 01:02:20 PM EDT
                                         No I hadn't, thanks - (ben_tilly) - Oct. 8, 2004, 01:08:02 PM EDT
                 BTW Arkadiy, I'm still waiting for a response - (ben_tilly) - (13) - Oct. 8, 2004, 12:57:52 PM EDT
                     I am not saying it's shorter in C... - (Arkadiy) - (10) - Oct. 8, 2004, 03:22:09 PM EDT
                         And now for my real comment - (ben_tilly) - (2) - Oct. 8, 2004, 03:34:09 PM EDT
                             May be it's a hindsight thing - (Arkadiy) - (1) - Oct. 8, 2004, 03:47:36 PM EDT
                                 It could be many things - (ben_tilly) - Oct. 8, 2004, 06:13:45 PM EDT
                         I don't know - multimap - (Simon_Jester) - (6) - Oct. 9, 2004, 12:22:32 AM EDT
                             Re: I don't know - multimap - (Arkadiy) - (5) - Oct. 9, 2004, 12:17:47 PM EDT
                                 Why the worry about efficiency? - (ben_tilly) - (4) - Oct. 9, 2004, 12:25:52 PM EDT
                                     I worry about efficiency - (Arkadiy) - (1) - Oct. 9, 2004, 12:30:44 PM EDT
                                         Ah - (ben_tilly) - Oct. 9, 2004, 12:59:07 PM EDT
                                     C vs Perl - efficiency - untrue for me - (broomberg) - (1) - Oct. 9, 2004, 12:41:13 PM EDT
                                         Point - but you may want to rebenchmark - (ben_tilly) - Oct. 9, 2004, 01:11:47 PM EDT
                     Here's a smalltalk version - (tuberculosis) - (1) - Oct. 8, 2004, 06:16:21 PM EDT
                         Yes, think of a reference as a pointer - (ben_tilly) - Oct. 8, 2004, 06:43:04 PM EDT

Kind of greenish blue, but not as greenish as, say, teal.
80 ms