A Simple Question From A Simple Man

TinkerTantrum has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: A Simple Question From A Simple Man by kcott (Archbishop) on Oct 10, 2012 at 23:19 UTC
G'day TinkerTantrum, Welcome to the monastery. In your code, `$rocks` and `@rocks` are two entirely different variables. Variables with a `$` are scalar values; those with an `@` are arrays. When you use brackets (`[]`) in the manner shown in your code, you are creating a reference to an array (typically just called an arrayref) - that's what `ARRAY(0x1434d80)` is referring to. You can also get a reference to an array by putting a backslash in front of the array name (e.g. `\@array_name`). You can access elements of an array with this syntax: `$array_name[index]` (where `index` is an integer). You can access elements of an arrayref with this syntax: `$array_ref->[index]` (again, `index` is an integer). Here's an extension to the code you posted showing all of these: `$ perl -le ' use warnings; $rocks = [1..23]; @rocks = qw/hail slate poop drop/; print $rocks; print $rocks->[0]; print \@rocks; print $rocks[0]; ' ARRAY(0x7fe363803ae8) 1 ARRAY(0x7fe36382b108) hail` [download] Have a read through these documentation pages for a more in-depth description: perlintro, perldata and perlref. You should also declare your variables. my is the most frequently used way of doing this - perlsub has a lot more information about this and other ways to declare variables. In addition to `use warnings;`, you should also add `use strict;` to the start of your code: this is one of the first things you'll read about in perlintro; details can be found in strict. Finally, if you just want to "get some interaction going with my fellow Monks", you can use the Chatterbox (typically referred to as the CB) which should be on the panel to your right. -- Ken	[reply] [d/l] [select]
Re^2: A Simple Question From A Simple Man by TinkerTantrum (Novice) on Oct 10, 2012 at 23:55 UTC
Aha! It all makes sense now. Thank you for the insight Mr. kcott. I must return to the dojo and meditate on this. You have been a true help!	[reply]
Re: A Simple Question From A Simple Man by Anonymous Monk on Oct 10, 2012 at 23:13 UTC
@rocks is an array, and $rocks is a scalar (an arrayref), they are different variables, they are not the same If you had used strict you would have been warned See Tutorials Data Types and Variables,the basic datatypes, three	[reply]
Re: A Simple Question From A Simple Man by Anonymous Monk on Oct 11, 2012 at 04:56 UTC
This notion of "a reference" ("arrayref" is slang for "a reference to an array," etc.) is one of the most-important concepts in Perl. A reference is a single value ... what's called a "scalar" ... yet it can refer to anything at all. For example, even though arrays are one-dimensional, every slot in it could consist of a reference to another array, thus creating a n-dimensional array, and so on. "Contexts" (array, hash, scalar, etc.), as denoted by characters "@", "$", "%" and so on, are also a very important idea.	[reply]
Re^2: A Simple Question From A Simple Man by TinkerTantrum (Novice) on Oct 14, 2012 at 02:32 UTC
So what you are saying (if I'm right) is that an "arrayref" can be treated as a scalar?	[reply]
Re^3: A Simple Question From A Simple Man by Athanasius (Cardinal) on Oct 14, 2012 at 03:37 UTC
No, an array reference is a scalar: `my @array = ('Matthew', 'Mark', 'Luke', 'John'); my $array_ref = \@array; my @new_array = @{ $array_ref }; print join(', ', @new_array);` [download] Here, `@array` is an array, as indicated by the “`@`” sigil, and `$array_ref` is a scalar, as per the “`$`” sigil. The syntax `@{ ... }` takes an array reference (which must be a scalar), and dereferences it to get the array it references. Here is something to meditate on: In Perl, an array can contain any number of elements, but each element must be a scalar. So, to make complex data structures (like N-dimensional arrays or arrays of hashes) you need some way of getting non-scalars (arrays or hashes) to act as scalars so they can be elements in the larger array. Which is where references come in: they are scalars which can be used to access other things, and those other things can be non-scalars. In addition to the reading recommendations given above by other monks, you might want to check out the Monastery’s tutorial intro to references. Hope that helps, Athanasius <°(((>< contra mundum	[reply] [d/l]