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authorDan Book <grinnz@gmail.com>2015-12-13 18:03:47 -0500
committerDan Book <grinnz@gmail.com>2015-12-13 18:03:47 -0500
commit0b8a0526249264c7ac34069adf3159f2b72771a8 (patch)
tree7c6b91c428cc7b93dd32f3410a7b80c654e084c5 /perl.html.markdown
parent18b3fb08a84171810c8e6f2e6fae5939c4428c04 (diff)
Add info on references, modules, and objects
These topics are central to modern usage of Perl.
Diffstat (limited to 'perl.html.markdown')
-rw-r--r--perl.html.markdown132
1 files changed, 125 insertions, 7 deletions
diff --git a/perl.html.markdown b/perl.html.markdown
index 1b86f410..85f3974e 100644
--- a/perl.html.markdown
+++ b/perl.html.markdown
@@ -5,6 +5,7 @@ language: perl
filename: learnperl.pl
contributors:
- ["Korjavin Ivan", "http://github.com/korjavin"]
+ - ["Dan Book", "http://github.com/Grinnz"]
---
Perl 5 is a highly capable, feature-rich programming language with over 25 years of development.
@@ -14,7 +15,6 @@ Perl 5 runs on over 100 platforms from portables to mainframes and is suitable f
```perl
# Single line comments start with a number sign.
-
#### Perl variable types
# Variables begin with a sigil, which is a symbol showing the type.
@@ -37,7 +37,9 @@ my @animals = ("camel", "llama", "owl");
my @numbers = (23, 42, 69);
my @mixed = ("camel", 42, 1.23);
-
+# Array elements are accessed using square brackets, with a $ to indicate
+# one value will be returned.
+my $second = $animals[1];
## Hashes
# A hash represents a set of key/value pairs:
@@ -50,11 +52,39 @@ my %fruit_color = (
apple => "red",
banana => "yellow",
);
+
+# Hash elements are accessed using curly braces, again with the $ sigil.
+my $color = $fruit_color{apple};
+
# Scalars, arrays and hashes are documented more fully in perldata.
# (perldoc perldata).
-# More complex data types can be constructed using references, which allow you
-# to build lists and hashes within lists and hashes.
+#### References
+
+# More complex data types can be constructed using references, which allow
+# you to build arrays and hashes within arrays and hashes.
+
+my $array_ref = \@array;
+my $hash_ref = \%hash;
+my @array_of_arrays = (\@array1, \@array2, \@array3);
+
+# You can also create anonymous arrays or hashes, returning a reference:
+
+my $fruits = ["apple", "banana"];
+my $colors = {apple => "red", banana => "yellow"};
+
+# References can be dereferenced by prefixing the appropriate sigil.
+
+my @fruits_array = @$fruits;
+my %colors_hash = %$colors;
+
+# As a shortcut, the arrow operator can be used to dereference and access a
+# single value.
+
+my $first = $array_ref->[0];
+my $value = $hash_ref->{banana};
+
+# See perlreftut and perlref for more in-depth documentation on references.
#### Conditional and looping constructs
@@ -105,6 +135,9 @@ for (@elements) {
# the Perlish post-condition way again
print for @elements;
+# iterating through the keys and values of a referenced hash
+print $hash_ref->{$_} for keys %$hash_ref;
+
#### Regular expressions
# Perl's regular expression support is both broad and deep, and is the subject
@@ -151,11 +184,96 @@ sub logger {
# Now we can use the subroutine just as any other built-in function:
logger("We have a logger subroutine!");
-```
-#### Using Perl modules
+#### Modules
+
+# A module is a set of Perl code, usually subroutines, which can be used in
+# other Perl code. It is usually stored in a file with the extension .pm so
+# that Perl can find it.
+
+package MyModule;
+
+sub trim {
+ my $string = shift;
+ $string =~ s/^\s+//;
+ $string =~ s/\s+$//;
+ return $string;
+}
+
+1;
+
+# From elsewhere:
+
+use MyModule;
+MyModule::trim($string);
+
+# The Exporter module can help with making subroutines exportable, so they
+# can be used like this:
+
+use MyModule 'trim';
+trim($string);
+
+# Many Perl modules can be downloaded from CPAN (http://www.cpan.org/) and
+# provide a range of features to help you avoid reinventing the wheel. A
+# number of popular modules like Exporter are included with the Perl
+# distribution itself. See perlmod for more details on modules in Perl.
+
+#### Objects
+
+# Objects in Perl are just references that know which class (package) they
+# belong to, so that methods (subroutines) called on it can be found there.
+# The bless function is used in constructors (usually new) to set this up.
+# However, you never need to call it yourself if you use a module like Moose
+# or Moo (see below).
+
+package MyCounter;
+
+sub new {
+ my $class = shift;
+ my $self = {count => 0};
+ return bless $self, $class;
+}
+
+sub count {
+ my $self = shift;
+ return $self->{count};
+}
+
+sub increment {
+ my $self = shift;
+ $self->{count}++;
+}
+
+1;
+
+# Methods can be called on a class or object instance with the arrow operator.
+
+my $counter = MyCounter->new;
+print $counter->count, "\n"; # 0
+$counter->increment;
+print $counter->count, "\n"; # 1
+
+# The modules Moose and Moo from CPAN can help you set up your object classes.
+# They provide a constructor and simple syntax for declaring attributes. This
+# class can be used equivalently to the one above.
+
+package MyCounter;
+use Moo;
+
+has 'count' => (is => 'rwp', default => 0, init_arg => undef);
+
+sub increment {
+ my $self = shift;
+ $self->_set_count($self->count + 1);
+}
+
+1;
+
+# Object-oriented programming is covered more thoroughly in perlootut, and its
+# low-level implementation in Perl is covered in perlobj.
+```
-Perl modules provide a range of features to help you avoid reinventing the wheel, and can be downloaded from CPAN (http://www.cpan.org/). A number of popular modules are included with the Perl distribution itself.
+#### FAQ
perlfaq contains questions and answers related to many common tasks, and often provides suggestions for good CPAN modules to use.