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 <https://github.com/Ovid/Corinna>.

    The keywords: "class", "field", "method".

    The attributes: "isa", "reader", "writer", "common".

    Only the "rw" attribute is got from Raku <https://www.raku.org>, 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.