Name

Class::Plain - a class syntax for the hash-based Perl OO.

Usage

  use Class::Plain;
  
  class Point {
    field x;
    field y;
    
    method new : common {
      my $self = $class->SUPER::new(@_);
      
      $self->{x} //= 0;
      $self->{y} //= 0;
      
      return $self;
    }
    
    method move {
      my ($x, $y) = @_;
      
      $self->{x} += $x;
      $self->{y} += $y;
    }
    
    method describe {
      print "A point at ($self->{x}, $self->{y})\n";
    }
  }
  
  my $point = Point->new(x => 5, y => 10);
  $point->describe;

Inheritance:

  class Point3D : isa(Point) {
    field z;
    
    method new : common {
      my $self = $class->SUPER::new(@_);
      
      $self->{z} //= 0;
      
      return $self;
    }
    
    method move {
      my ($x, $y, $z) = @_;
      
      $self->SUPER::move($x, $y);
      $self->{z} += $z;
    }
    
    method describe {
      print "A point at ($self->{x}, $self->{y}, $self->{z})\n";
    }
  }
  
  my $point3d = Point3D->new(x => 5, y => 10, z => 15);
  $point3d->describe;

See also Class Plain Cookbook.

Description

This module provides a class syntax for the hash-based Perl OO.

Keywords

class

  class NAME { ... }

  class NAME : ATTRS... {
    ...
  }

  class NAME;

  class NAME : ATTRS...;

Behaves similarly to the package keyword, but provides a package that defines a new class.

As with package, an optional block may be provided. If so, the contents of that block define the new class and the preceding package continues afterwards. If not, it sets the class as the package context of following keywords and definitions.

The following class attributes are supported:

isa Attribute

 # The single inheritance
 : isa(SUPER_CLASS)
 
 # The multiple inheritance
 : isa(SUPER_CLASS1) isa(SUPER_CLASS2)
 
 # The super class is nothing
 : isa()

Define a supper classes that this class extends.

If the supper class is not specified by isa attribute, the class inherits Class::Plain::Base.

The super class is added to the end of @ISA.

If the the super class name doesn't exists in the Perl's symbol table, the super class is loaded.

Otherwise if the super class doesn't have the new method and doesn't have the class names in @ISA, the super class is loaded.

field

  field NAME;
  
  field NAME : ATTR ATTR...;

Define fields.

The following field attributes are supported:

reader Attribute

  : reader
  
  : reader(METHOD_NAME)

Generates a reader method to return the current value of the field. If no name is given, the name of the field is used.

  field x : reader;

  # This is the same as the following code.
  method x {
    $self->{x};
  }

The different method name can be specified.

  field x : reader(x_different_name);

writer Attribute

  : writer

  : writer(METHOD_NAME)

Generates a writer method to set a new value of the field from its arguments. If no name is given, the name of the field is used prefixed by set_.

  field x : writer;

  # This is the same as the following code.
  method set_x {
    $self->{x} = shift;
    return $self;
  }

The different method name can be specified.

  field x : writer(set_x_different_name);

rw Attribute

  : rw

  : rw(METHOD_NAME)

Generates a read-write method to set and get the value of the field. If no name is given, the name of the field is used.

  field x : rw;

  # This is the same as the following code.
  method x {
    if (@_) {
      $self->{x} = shift;
      return $self;
    }
    $self->{x};
  }

The different method name can be specified.

  field x : rw(x_different_name);

method

  method NAME {
     ...
  }

  method NAME : ATTR ATTR ... {
     ...
  }

Define a new named method. This behaves similarly to the sub keyword. In addition, the method body will have a lexical called $self which contains the invocant object directly; it will already have been shifted from the @_ array.

The following method attributes are supported.

Examples:

  # An instance method
  method to_string {
    
    my $string = "($self->{x},$self->{y})";
    
    return $string;
  }

common Attribute

  : common

Marks that this method is a class-common method, instead of a regular instance method. A class-common method may be invoked on class names instead of instances. Within the method body there is a lexical $class available instead of $self. It will already have been shifted from the @_ array.

Examples:

  # A class method
  method new : common {
    my $self = $class->SUPER::new(@_);
    
    # ...
    
    return $self;
  }

Required Perl Version

Perl 5.16+.

Cookbook

Exmples of Class::Plain.

Class::Plain::Document::Cookbook

See Also

Object::Pad

The implementation of the Class::Plain module is started from the copy of the source code of Object::Pad.

Corinna

Class::Plain uses the keywords and attributes that are specified in Corinna.

The keywords: class, field, method.

The attributes: isa, reader, writer, common.

Only the rw attribute is got from Raku, Moo, Moose.

XS::Parse::Keyword

The class and field keywords are parsed by XS::Parse::Keyword.

XS::Parse::Sublike

The method keyword is parsed by XS::Parse::Sublike.

cpanm Class::Plain

perl -MCPAN -e shell
install Class::Plain