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  CUR = 2
  LEN = 16
  COW_REFCNT = 1
SV = PV(0xb400007267a2e0b0) at 0xb400007267a1f948
  REFCNT = 1
  FLAGS = (POK,IsCOW,pPOK)
  PV = 0xb4000071e76df8b0 ""\0
  CUR = 0
  LEN = 16
  COW_REFCNT = 1
SV = PV(0xb400007267a2dea0) at 0xb400007267a1f930
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0xb4000071e774e170 "\xD7\x90"\0
  CUR = 2
  LEN = 16

# Display ALEF from different ways.
perl -C -E 'say "\N{HEBREW LETTER ALEF}"'   א
perl -C -E 'say "\N{U+5d0}"'                א
perl -C -E 'say "\x{5d0}"'                  א
perl -C -E 'say chr(0x5d0)'                 א
perl -C -E 'say chr(0x05d0)'                א
perl -C -E 'say chr(1488)'                  א
perl -C -E 'say v1488'                      א

# To and from Unicode code point and unnicode byte stream.
perl -C -Me -e 'say unpack "H*", enc "\x{5d0}"'
d790
#
perl -C -Me -e 'say unpack "U*", "\x{5d0}"'
1488


#############################################################
## Perl Object (before class keyword)
#############################################################

# Different ways to check if an object is a certain class.
perl -E 'my $v = 1; say ref $v'
perl -E 'my $v = bless {}, "Cat"; say ref $v'
perl -E 'my $v = bless {}, "Cat"; say $v isa "Cat"'
perl -E 'my $v = bless {}, "Cat"; say $v->isa("Cat")'
perl -E 'my $v = bless {}, "Cat"; say UNIVERSAL::isa($v,"Cat")'


#############################################################
## Perl Class Keyword
#############################################################

# Since 5.38.0, can use 'class' instead of 'package' for a postmodern OOP.
# Perl class documentation.
perlbrew use perl-5.38.0
perldoc class

# Simple example using perl class.
perl -E 'use feature qw(class); no warnings qw(experimental::class); class Point { field $x :param; method show { say $x } } Point->new(x => 333)->show'
333

# Using a different name for the parameter.
perl -E 'use feature ":all"; no warnings "experimental::class"; class Point 1.2 { field $x :param(_x); method show { say $x } } Point->new(_x => 111)->show'
111

# Perl class - class block/statement.
#
# Block form:
perl -E 'use experimental "class"; class C { field $name = "bob"; method say_hi(){ say "Hi $name" } } C->new->say_hi'
Hi bob
#
# Statement form:
perl -E 'use experimental "class"; class C; field $name = "bob"; method say_hi(){ say "Hi $name" } package main; C->new->say_hi'
Hi bob

# Perl class - fields.
#
# Cannot access field outside.
perl -E 'use experimental "class"; class C { field $id } say C->new'
#
# field vs my.
perl -E 'use experimental "class"; class C { my $count = 1; field $id = $count++; method id { $id } } say C->new->id; say C->new->id;'
1
2

# Perl class - :param field attribute.
#
# There is a check to present unrecognised data from being passed to the constructor.
perl -E 'use experimental "class"; class C { field $id; method id { $id } } say C->new( id => 123)->id'
Unrecognised parameters for "C" constructor: id at -e line 1.
#
# Use :param to allow setting that field.
perl -E 'use experimental "class"; class C { field $id :param; method id { $id } } say C->new( id => 123)->id'
123
#
# The :param attribute by deault makes the parameter to be required.
perl -E 'use experimental "class"; class C { field $id :param; method id { $id } } say C->new->id'
Required parameter 'id' is missing for "C" constructor at -e line 1.

# Perl class - :param field attribute.
# Specify a default for a required parameter class.
#
# :param =
perl -E 'use experimental "class"; class C { field $id :param = "ZZZ"; method id { $id } } say C->new->id'
ZZZ
perl -E 'use experimental "class"; class C { field $id :param = "ZZZ"; method id { $id } } say C->new( id => 111)->id'
111
perl -E 'use experimental "class"; class C { field $id :param = "ZZZ"; method id { $id } } say C->new( id => undef )->id'
[empty]
#
# :param //=
perl -E 'use experimental "class"; class C { field $id :param //= "ZZZ"; method id { $id } } say C->new( id => undef )->id'
ZZZ
perl -E 'use experimental "class"; class C { field $id :param //= "ZZZ"; method id { $id } } say C->new( id => 0 )->id'
0
#
# :param ||=
perl -E 'use experimental "class"; class C { field $id :param ||= "ZZZ"; method id { $id } } say C->new( id => 0 )->id'
ZZZ
perl -E 'use experimental "class"; class C { field $id :param ||= "ZZZ"; method id { $id } } say C->new( id => 111 )->id'
111

# Perl class - method statement.