On 12/24/2011 08:54 AM, lina wrote:
Did not notice the difference between () and {} in tutorial.
Perl is the most complex and subtle programming language/ system I know (attempt?). For example, see the following Perl script which demonstrates syntax for accessing single and multiple (slice) elements of an array using basic types, functions, and simple OO.
As you can see, there's more than one way to do it (TIMTOWTDI). (And, probably more than I found.) There are even more ways that appear correct upon casual coding, but either generate errors/ warnings (lucky you) or have some subtle bug (you poor slob). (My example surely contains the later.) Once you find enough no-error-or-warning-message choices and lay them out side by side, some method to the madness can be observed. But, finding all the possibilities, finding a choice you like, or even just finding a choice that works can be very daunting, especially when faced with a blank screen.
Now, imagine what happens when you add multi-level data structures, tied variables, additional OO (polymorphism, operator overloading, multiple inheritance, roles, delegates, method modifiers, etc.), meta-programming, higher-order functions, and/or other Perl capabilities.
Understand that there is no specification for Perl 5; the implementation and regression tests serve as the de facto standard. So, finding the rules for enumerating all the correct possibilities for a given decision means analyzing the source code of Perl itself. I'm not going there.
As best I can figure, writing a computer program involves making some number, N, of key decisions. With a Python motto, you make 1**N = N decisions and you're done. With a Perl motto and M choices per decision, you need to explore M**N possibilities. Both presume at least one correct choice for each decision. (That's why a comprehensive and high-quality library is required for a language/ system to be "general purpose" and generally usable.)
With practice and experience, I've come up with favorite choices for the most common decisions I've faced (using whatever subset of each M I could find). These choices are incorporated throughout the libraries and programs I maintain. But, as I push harder and reach higher, new capabilities often force me to re-evaluate prior decisions. Foundational changes, such as abandoning my home-grown logging system and switching to Log::Log4Perl, create domino effects. Now I'm learning Moose (the Perl 6 advanced OO system back-ported to Perl 5) and foresee a lot of work.
David -- 2011-12-24 11:29:16 dpchrist@p43400e ~/sandbox/perl $ cat /etc/debian_version 6.0.3 2011-12-24 11:29:20 dpchrist@p43400e ~/sandbox/perl $ perl -v This is perl, v5.10.1 (*) built for i486-linux-gnu-thread-multi (with 53 registered patches, see perl -V for more detail) Copyright 1987-2009, Larry WallPerl may be copied only under the terms of either the Artistic License or the
GNU General Public License, which may be found in the Perl 5 source kit. Complete documentation for Perl, including FAQ lists, should be found on this system using "man perl" or "perldoc perl". If you have access to the Internet, point your browser at http://www.perl.org/, the Perl Home Page. 2011-12-24 11:29:25 dpchrist@p43400e ~/sandbox/perl $ cat array-slice.pl #!/usr/bin/perl # $Id: array-slice.pl,v 1.2 2011-12-24 19:29:15 dpchrist Exp $ ### enforce clean code and autoflush output: use strict; use warnings; $| = 1; ### define a class that holds an array: package MyArray; sub new { my $class = shift; return bless [@_], $class } sub a { my $self = shift; return @$self } sub ra { my $self = shift; return [@$self] } ### main script: package main; ### pull in some helpful modules: use Array::Utils ':all'; use Data::Dumper; $Data::Dumper::Indent = 0; use Test::More tests => 45; ### define array and contents: my @a = qw( a b c d e f ); ### define reference to array: my $ra = \@a; ### define function that returns array contents: sub fa { @a }; ### define function that returns reference to array: sub fra { $ra }; ### allocate object that contains a copy of array contents: my $oa = MyArray->new(@a); ### define expected results of tests: my $a = [qw( a )]; my $abc = [qw( a b c )]; my $abcdef = [qw( a b c d e f )]; my $rxA = 'ARRAY\(0x[0-9a-g]{7}\)'; ### shopping list of test code and expected values: my @code_exp = ( '@a', $abcdef, # 1 '$a[0]', $a, # 2 '@a[0, 1, 2]', $abc, # 3 '@a[0 .. 2]', $abc, # 4 '@{$ra}', $abcdef, # 5 '$ra->[0]', $a, # 6 '@{$ra}[0, 1, 2]', $abc, # 7 '@{$ra}[0 .. 2]', $abc, # 8 '(@{$ra})[0, 1, 2]', $abc, # 9 '(@{$ra})[0 .. 2]', $abc, # 10 '@$ra', $abcdef, # 11 '(@$ra)[0, 1, 2]', $abc, # 12 '(@$ra)[0 .. 2]', $abc, # 13 '&fa()', $abcdef, # 14 '&fa', $abcdef, # 15 'fa()', $abcdef, # 16 'fa', $abcdef, # 17 '(fa)[0]', $a, # 18 '(fa)[0, 1, 2]', $abc, # 19 '(fa)[0 .. 2]', $abc, # 20 '&fra()', $rxA, # 21 '&fra', $rxA, # 22 'fra()', $rxA, # 23 'fra', $rxA, # 24 '@{&fra()}', $abcdef, # 25 '@{&fra}', $abcdef, # 26 '@{fra()}', $abcdef, # 27 '@{+fra}', $abcdef, # 28 'fra->[0]', $a, # 29 '@{fra()}[0, 1, 2]', $abc, # 30 '@{fra()}[0 .. 2]', $abc, # 31 '@{&fra()}[0, 1, 2]', $abc, # 32 '@{&fra}[0, 1, 2]', $abc, # 33 '@{fra()}[0, 1, 2]', $abc, # 34 '@{+fra}[0, 1, 2]', $abc, # 35 '$oa->a', $abcdef, # 36 '($oa->a)[0]', $a, # 37 '($oa->a)[0, 1, 2]', $abc, # 38 '($oa->a)[0 .. 2]', $abc, # 39 '$oa->ra', $rxA, # 40 '$oa->ra->[0]', $a, # 41 '@{$oa->ra}[0, 1, 2]', $abc, # 42 '@{$oa->ra}[0 .. 2]', $abc, # 43 '(@{$oa->ra})[0, 1, 2]', $abc, # 44 '(@{$oa->ra})[0 .. 2]', $abc, # 45 ); ### test engine: while (@code_exp) { my $code = shift @code_exp; my $exp = shift @code_exp; my $got = [ eval $code ]; my $ok = (ref($exp) eq 'ARRAY') ? !array_diff(@$got, @$exp) : $got =~ qr/$exp/; my $msg = sprintf("%-20s %s", $code, ( ref($exp) eq 'ARRAY' ? join(' ', @$exp) : 'qr/' . $exp . '/' ), ); ok($ok, $msg) or warn Data::Dumper->Dump([$got], [qw(got)]); } 2011-12-24 11:29:31 dpchrist@p43400e ~/sandbox/perl $ perl array-slice.pl 1..45 ok 1 - @a a b c d e f ok 2 - $a[0] a ok 3 - @a[0, 1, 2] a b c ok 4 - @a[0 .. 2] a b c ok 5 - @{$ra} a b c d e f ok 6 - $ra->[0] a ok 7 - @{$ra}[0, 1, 2] a b c ok 8 - @{$ra}[0 .. 2] a b c ok 9 - (@{$ra})[0, 1, 2] a b c ok 10 - (@{$ra})[0 .. 2] a b c ok 11 - @$ra a b c d e f ok 12 - (@$ra)[0, 1, 2] a b c ok 13 - (@$ra)[0 .. 2] a b c ok 14 - &fa() a b c d e f ok 15 - &fa a b c d e f ok 16 - fa() a b c d e f ok 17 - fa a b c d e f ok 18 - (fa)[0] a ok 19 - (fa)[0, 1, 2] a b c ok 20 - (fa)[0 .. 2] a b c ok 21 - &fra() qr/ARRAY\(0x[0-9a-g]{7}\)/ ok 22 - &fra qr/ARRAY\(0x[0-9a-g]{7}\)/ ok 23 - fra() qr/ARRAY\(0x[0-9a-g]{7}\)/ ok 24 - fra qr/ARRAY\(0x[0-9a-g]{7}\)/ ok 25 - @{&fra()} a b c d e f ok 26 - @{&fra} a b c d e f ok 27 - @{fra()} a b c d e f ok 28 - @{+fra} a b c d e f ok 29 - fra->[0] a ok 30 - @{fra()}[0, 1, 2] a b c ok 31 - @{fra()}[0 .. 2] a b c ok 32 - @{&fra()}[0, 1, 2] a b c ok 33 - @{&fra}[0, 1, 2] a b c ok 34 - @{fra()}[0, 1, 2] a b c ok 35 - @{+fra}[0, 1, 2] a b c ok 36 - $oa->a a b c d e f ok 37 - ($oa->a)[0] a ok 38 - ($oa->a)[0, 1, 2] a b c ok 39 - ($oa->a)[0 .. 2] a b c ok 40 - $oa->ra qr/ARRAY\(0x[0-9a-g]{7}\)/ ok 41 - $oa->ra->[0] a ok 42 - @{$oa->ra}[0, 1, 2] a b c ok 43 - @{$oa->ra}[0 .. 2] a b c ok 44 - (@{$oa->ra})[0, 1, 2] a b c ok 45 - (@{$oa->ra})[0 .. 2] a b c --To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
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