Class: Class

Inherits:

Module

• Object
• Module
• Class

Defined in:

object.c,
class.c,
object.c

Overview

Classes in Ruby are first-class objects—each is an instance of class Class.

Typically, you create a new class by using:

class Name
 # some code describing the class behavior
end

When a new class is created, an object of type Class is initialized and assigned to a global constant (Name in this case).

When Name.new is called to create a new object, the new method in Class is run by default. This can be demonstrated by overriding new in Class:

class Class
  alias old_new new
  def new(*args)
    print "Creating a new ", self.name, "\n"
    old_new(*args)
  end
end

class Name
end

n = Name.new

produces:

Creating a new Name

Classes, modules, and objects are interrelated. In the diagram that follows, the vertical arrows represent inheritance, and the parentheses metaclasses. All metaclasses are instances of the class ‘Class’.

                         +---------+             +-...
                         |         |             |
         BasicObject-----|-->(BasicObject)-------|-...
             ^           |         ^             |
             |           |         |             |
          Object---------|----->(Object)---------|-...
             ^           |         ^             |
             |           |         |             |
             +-------+   |         +--------+    |
             |       |   |         |        |    |
             |    Module-|---------|--->(Module)-|-...
             |       ^   |         |        ^    |
             |       |   |         |        |    |
             |     Class-|---------|---->(Class)-|-...
             |       ^   |         |        ^    |
             |       +---+         |        +----+
             |                     |
obj--->OtherClass---------->(OtherClass)-----------...

Instance Method Summary

• #allocate ⇒ Object

  Allocates space for a new object of class’s class and does not call initialize on the new instance.

• #inherited ⇒ Object private

  Not documented.

• #initialize(*args) ⇒ Object constructor

  Creates a new anonymous (unnamed) class with the given superclass (or Object if no parameter is given).

• #new(args, ...) ⇒ Object

  Calls allocate to create a new object of class’s class, then invokes that object’s initialize method, passing it args.

• #superclass ⇒ nil

  Returns the superclass of class, or nil.

Methods inherited from Module

#<, #<=, #<=>, #==, #===, #>, #>=, #alias_method, #ancestors, #append_features, #attr, #attr_accessor, #attr_reader, #attr_writer, #autoload, #autoload?, #class_eval, #class_exec, #class_variable_defined?, #class_variable_get, #class_variable_set, #class_variables, #const_defined?, #const_get, #const_missing, #const_set, #constants, constants, #define_method, #extend_object, #extended, #freeze, #include, #include?, #included, #included_modules, #initialize_clone, #initialize_copy, #instance_method, #instance_methods, #method_added, #method_defined?, #method_removed, #method_undefined, #module_eval, #module_exec, #module_function, #name, nesting, #prepend, #prepend_features, #prepended, #private, #private_class_method, #private_constant, #private_instance_methods, #private_method_defined?, #protected, #protected_instance_methods, #protected_method_defined?, #public, #public_class_method, #public_constant, #public_instance_method, #public_instance_methods, #public_method_defined?, #refine, #remove_class_variable, #remove_const, #remove_method, #singleton_class?, #to_s, #undef_method, #using

Constructor Details

#new(super_class = Object) ⇒ Class #new(super_class = Object) {|mod| ... } ⇒ Class

Creates a new anonymous (unnamed) class with the given superclass (or Object if no parameter is given). You can give a class a name by assigning the class object to a constant.

If a block is given, it is passed the class object, and the block is evaluated in the context of this class using class_eval.

fred = Class.new do
  def meth1
    "hello"
  end
  def meth2
    "bye"
  end
end

a = fred.new     #=> #<#<Class:0x100381890>:0x100376b98>
a.meth1          #=> "hello"
a.meth2          #=> "bye"

Assign the class to a constant (name starting uppercase) if you want to treat it like a regular class.

Overloads:

• #new(super_class = Object) ⇒ Class
• #new(super_class = Object) {|mod| ... } ⇒ Class

  Yields:

  • (mod)

# File 'object.c', line 1748

static VALUE
rb_class_initialize(int argc, VALUE *argv, VALUE klass)
{
    VALUE super;

    if (RCLASS_SUPER(klass) != 0 || klass == rb_cBasicObject) {
	rb_raise(rb_eTypeError, "already initialized class");
    }
    if (argc == 0) {
	super = rb_cObject;
    }
    else {
	rb_scan_args(argc, argv, "01", &super);
	rb_check_inheritable(super);
	if (super != rb_cBasicObject && !RCLASS_SUPER(super)) {
	    rb_raise(rb_eTypeError, "can't inherit uninitialized class");
	}
    }
    RCLASS_SET_SUPER(klass, super);
    rb_make_metaclass(klass, RBASIC(super)->klass);
    rb_class_inherited(super, klass);
    rb_mod_initialize(klass);

    return klass;
}

Instance Method Details

#allocate ⇒ Object

Allocates space for a new object of class’s class and does not call initialize on the new instance. The returned object must be an instance of class.

klass = Class.new do
  def initialize(*args)
    @initialized = true
  end

  def initialized?
    @initialized || false
  end
end

klass.allocate.initialized? #=> false

Returns:

• (Object)

# File 'object.c', line 1796

VALUE
rb_obj_alloc(VALUE klass)
{
    VALUE obj;
    rb_alloc_func_t allocator;

    if (RCLASS_SUPER(klass) == 0 && klass != rb_cBasicObject) {
	rb_raise(rb_eTypeError, "can't instantiate uninitialized class");
    }
    if (FL_TEST(klass, FL_SINGLETON)) {
	rb_raise(rb_eTypeError, "can't create instance of singleton class");
    }
    allocator = rb_get_alloc_func(klass);
    if (!allocator) {
	rb_raise(rb_eTypeError, "allocator undefined for %"PRIsVALUE,
		 klass);
    }

#if !defined(DTRACE_PROBES_DISABLED) || !DTRACE_PROBES_DISABLED
    if (RUBY_DTRACE_OBJECT_CREATE_ENABLED()) {
        const char * file = rb_sourcefile();
        RUBY_DTRACE_OBJECT_CREATE(rb_class2name(klass),
				  file ? file : "",
				  rb_sourceline());
    }
#endif

    obj = (*allocator)(klass);

    if (rb_obj_class(obj) != rb_class_real(klass)) {
	rb_raise(rb_eTypeError, "wrong instance allocation");
    }
    return obj;
}

#inherited ⇒ Object (private)

Not documented

# File 'object.c', line 919

static VALUE
rb_obj_dummy(void)
{
    return Qnil;
}

#new(args, ...) ⇒ Object

Calls allocate to create a new object of class’s class, then invokes that object’s initialize method, passing it args. This is the method that ends up getting called whenever an object is constructed using .new.

Returns:

• (Object)

# File 'object.c', line 1850

VALUE
rb_class_new_instance(int argc, const VALUE *argv, VALUE klass)
{
    VALUE obj;

    obj = rb_obj_alloc(klass);
    rb_obj_call_init(obj, argc, argv);

    return obj;
}

#superclass ⇒ nil

Returns the superclass of class, or nil.

File.superclass          #=> IO
IO.superclass            #=> Object
Object.superclass        #=> BasicObject
class Foo; end
class Bar < Foo; end
Bar.superclass           #=> Foo

Returns nil when the given class does not have a parent class:

BasicObject.superclass   #=> nil

Returns:

• (nil)

# File 'object.c', line 1880

VALUE
rb_class_superclass(VALUE klass)
{
    VALUE super = RCLASS_SUPER(klass);

    if (!super) {
	if (klass == rb_cBasicObject) return Qnil;
	rb_raise(rb_eTypeError, "uninitialized class");
    }
    while (RB_TYPE_P(super, T_ICLASS)) {
	super = RCLASS_SUPER(super);
    }
    if (!super) {
	return Qnil;
    }
    return super;
}