class Class
Extends any Class to include json_creatable? method.
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)-----------...Public Class Methods
new(super_class=Object) → a_class Show source
new(super_class=Object) { |mod| ... } → a_class
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;
}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 like 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.
Public Instance Methods
allocate() → obj Show source
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_undefined_alloc(klass);
}
RUBY_DTRACE_CREATE_HOOK(OBJECT, rb_class2name(klass));
obj = (*allocator)(klass);
if (rb_obj_class(obj) != rb_class_real(klass)) {
rb_raise(rb_eTypeError, "wrong instance allocation");
}
return obj;
}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
# File ext/json/lib/json/common.rb, line 453
def json_creatable?
respond_to?(:json_create)
endReturns true if this class can be used to create an instance from a serialised JSON string. The class has to implement a class method json_create that expects a hash as first parameter. The hash should include the required data.
new(args, ...) → obj Show source
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;
}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.
superclass → a_super_class or nil Show source
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;
}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
Private Instance Methods
inherited(subclass) Show source
static VALUE
rb_obj_dummy(void)
{
return Qnil;
}Callback invoked whenever a subclass of the current class is created.
Example:
class Foo
def self.inherited(subclass)
puts "New subclass: #{subclass}"
end
end
class Bar < Foo
end
class Baz < Bar
end
produces:
New subclass: Bar
New subclass: Baz
Ruby Core © 1993–2017 Yukihiro Matsumoto
Licensed under the Ruby License.
Ruby Standard Library © contributors
Licensed under their own licenses.