On Mon, Nov 26, 2001 at 05:54:24PM -0500, [EMAIL PROTECTED] wrote:
I've modified the original email, and moved things around, for clarity.
> #========================================================
> #!/usr/bin/perl
> use strict;
> # IF I do not assign {}, nothing is printed
> my($hash) = {};
> &getArray($hash);
[snip]
> a) When a hash reference is essentially a SCALAR, why should I explicitly
> denote the hash variable as
> my($hash) = {};
> and not simply
> my($hash);
When you say getArray($hash), where $hash eq undef, you are effectively
passing $hash by value. $hash is not a reference, and therefore your
assignment and manipulation of it inside getArray() isn't going to be
visible outside of the subroutine.
When you say getArray($hash), where $hash is a hash reference, you are now
passing by reference, and modifications to $hash inside the subroutine
affect the original hash you passed in.
[snip]
> # IF I do not engulf array-ref within {} as @{$hash->{array}}
> # an error message NOT AN ARRAY reference is generated
> map {print "$_\n"} @{$hash->{array}};
>
> sub getArray{
> my($hash) = shift;
> $hash->{array} = [1,2,3,4,5];
> }
> #========================================================
[snip]
> b) I thought that an array can be dereferenced simply by @$arrayRef
> notation. However, in the code sample I have sent, I am forced to use
> @{$arrayRef} notation. Why do I need the Chain-braces?
It has to do with precedence. When you say:
print @$hash->{array}
you're basically saying:
my @tmp = @$hash;
print $tmp{array};
Which is, of course, incorrect, because you're accessing a hash, not an
array. You have to add the braces to clear up the ambiguity; that you want
to dereference $hash->{array} as an array.
Michael
--
Administrator www.shoebox.net
Programmer, System Administrator www.gallanttech.com
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