Re^7: Pointers and References

Lists in Perl are two things:

a syntax, mostly comma separated (, is a list operator)
a temporary stack to pass this sequence of scalars

Array is

a @variable holding
a data structure in memory

So @a = (1,2,3) means step by step

array variable @a at LHS forces a list assignment
the comma syntax denotes a list
the list values are pushed to a stack
the stack is assigned to the array and stored in memory in an AV

I hope it's clearer now.

If it's a consolation, Larry occasionally confused the terminology too, e.g. in wantarray :)

> (Modification of a read-only value attempted)

That's because 1,2,3 are literals which are read only. Use variables (sic) and you can change them in the loop. ;)

Cheers Rolf
_{(addicted to the Perl Programming Language :)

Wikisyntax for the Monastery}

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Re^8: Pointers and References by bliako (Abbot) on Nov 24, 2020 at 20:38 UTC
yep `use strict; use warnings; my $x = 12; foreach my $aa ($x,$x){ $aa = 13; } print $x; ---------- 13` [download] How about "readonly, anonymous stack" instead of list? Iam joking, enough of the nomenclature	[reply] [d/l]
Re^9: Pointers and References by AnomalousMonk (Archbishop) on Nov 24, 2020 at 22:18 UTC
And also for arrays: `Win8 Strawberry 5.8.9.5 (32) Tue 11/24/2020 17:09:57 C:\@Work\Perl\monks >perl -Mstrict -Mwarnings -l my $x = 1; my $y = 2; my @z = (3, 4, 5); $_ += 100 for @z, $x, $y; print "$x, $y, (@z)"; for ($x, @z, $y) { $_ += 100; } print "$x, $y, (@z)"; ^Z 101, 102, (103 104 105) 201, 202, (203 204 205)` [download] Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^9: Pointers and References by LanX (Saint) on Nov 25, 2020 at 13:55 UTC
I hope the distinction between list and arrays is clearer now, I know its confusing. E.g. this is a list assignment without literal list: `@a = %a` , ... the hash is unpacked into a list which is packed into an array. or here you need a literal list to init an array(-ref) : `$a_ref = [ 1,2,3 ]` Please feel free to ask. :) Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re^10: Pointers and References by bliako (Abbot) on Nov 25, 2020 at 16:08 UTC
Sure, thanks! I will ask if I have a problem.	[reply]
Re^8: Pointers and References by Leudwinus (Scribe) on Nov 25, 2020 at 15:33 UTC
That's because 1,2,3 are literals which are read only. Use variables (sic) and you can change them in the loop. ;) It took me a few times to understand this line based on the examples given further below but now this makes sense!	[reply]
Re^9: Pointers and References by LanX (Saint) on Nov 25, 2020 at 16:14 UTC
Perl is aliasing in for loops. So `$x = 42` is as useful as `1 = 42` HTH! :) Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re^10: Pointers and References (updated) by AnomalousMonk (Archbishop) on Nov 25, 2020 at 20:55 UTC
So $x = 42 is as useful as 1 = 42 I don't understand this statement. I can see where an expression like `$x = 42` might be useful, but `1 = 42` can't possibly be useful because it won't compile. Update: Or do you mean "if `$x` is aliased to a literal value (e.g., 1), `$x = 42` is equivalent to `1 = 42`"? (Update: And specifically WRT to the `for`-loop here? I didn't look back far enough. :) Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^11: Pointers and References (updated) by LanX (Saint) on Nov 25, 2020 at 21:21 UTC