Classes in Ruby are first-class objects—each is an instance of class Class.
When a new class is created (typically using class Name ... end), an object of type Class is created 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 oldNew new def new(*args) print "Creating a new ", self.name, "\n" oldNew(*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 meta-classes. All metaclasses are instances of the class `Class’.
+---------+ +-... | | | BasicObject-----|-->(BasicObject)-------|-... ^ | ^ | | | | | Object---------|----->(Object)---------|-... ^ | ^ | | | | | +-------+ | +--------+ | | | | | | | | Module-|---------|--->(Module)-|-... | ^ | | ^ | | | | | | | | Class-|---------|---->(Class)-|-... | ^ | | ^ | | +---+ | +----+ | | obj--->OtherClass---------->(OtherClass)-----------...
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.
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);
}
RCLASS_SUPER(klass) = super;
rb_make_metaclass(klass, RBASIC(super)->klass);
rb_class_inherited(super, klass);
rb_mod_initialize(klass);
return klass;
}
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
VALUE
rb_obj_alloc(VALUE klass)
{
VALUE obj;
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");
}
obj = rb_funcall(klass, ID_ALLOCATOR, 0, 0);
if (rb_obj_class(obj) != rb_class_real(klass)) {
rb_raise(rb_eTypeError, "wrong instance allocation");
}
return obj;
}
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.
VALUE
rb_class_new_instance(int argc, VALUE *argv, VALUE klass)
{
VALUE obj;
obj = rb_obj_alloc(klass);
rb_obj_call_init(obj, argc, argv);
return obj;
}
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 hasn’t a parent class:
BasicObject.superclass #=> nil
static 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 (TYPE(super) == T_ICLASS) {
super = RCLASS_SUPER(super);
}
if (!super) {
return Qnil;
}
return super;
}