Object is the parent class of all classes in Ruby. Its methods are therefore available to all objects unless explicitly overridden.
Object mixes in the Kernel module, making the built-in kernel functions globally accessible. Although the instance methods of Object are defined by the Kernel module, we have chosen to document them here for clarity.
In the descriptions of Object‘s methods, the parameter symbol refers to a symbol, which is either a quoted string or a Symbol (such as :name).
| TOPLEVEL_BINDING | = | rb_f_binding(ruby_top_self) | ||
| ENV | = | envtbl | ||
| ENV | = | envtbl | ||
| STDIN | = | rb_stdin | constants to hold original stdin/stdout/stderr | |
| STDOUT | = | rb_stdout | ||
| STDERR | = | rb_stderr | ||
| ARGF | = | argf | ||
| NIL | = | Qnil | ||
| TRUE | = | Qtrue | ||
| FALSE | = | Qfalse | ||
| MatchingData | = | rb_cMatch | ||
| DATA | = | f | ||
| ARGV | = | rb_argv | ||
| RUBY_VERSION | = | v | ||
| RUBY_RELEASE_DATE | = | d | ||
| RUBY_PLATFORM | = | p | ||
| RUBY_PATCHLEVEL | = | INT2FIX(RUBY_PATCHLEVEL) | ||
| RUBY_DESCRIPTION | = | tmp | ||
| RUBY_COPYRIGHT | = | tmp | ||
| VERSION | = | v | obsolete constants | |
| RELEASE_DATE | = | d | ||
| PLATFORM | = | p |
Equality—At the Object level, == returns true only if obj and other are the same object. Typically, this method is overridden in descendent classes to provide class-specific meaning.
Unlike ==, the equal? method should never be overridden by subclasses: it is used to determine object identity (that is, a.equal?(b) iff a is the same object as b).
The eql? method returns true if obj and anObject have the same value. Used by Hash to test members for equality. For objects of class Object, eql? is synonymous with ==. Subclasses normally continue this tradition, but there are exceptions. Numeric types, for example, perform type conversion across ==, but not across eql?, so:
1 == 1.0 #=> true 1.eql? 1.0 #=> false
Returns an integer identifier for obj. The same number will be returned on all calls to id for a given object, and no two active objects will share an id. Object#object_id is a different concept from the :name notation, which returns the symbol id of name. Replaces the deprecated Object#id.
Produces a shallow copy of obj—the instance variables of obj are copied, but not the objects they reference. Copies the frozen and tainted state of obj. See also the discussion under Object#dup.
class Klass
attr_accessor :str
end
s1 = Klass.new #=> #<Klass:0x401b3a38>
s1.str = "Hello" #=> "Hello"
s2 = s1.clone #=> #<Klass:0x401b3998 @str="Hello">
s2.str[1,4] = "i" #=> "i"
s1.inspect #=> "#<Klass:0x401b3a38 @str=\"Hi\">"
s2.inspect #=> "#<Klass:0x401b3998 @str=\"Hi\">"
This method may have class-specific behavior. If so, that behavior will be documented under the #initialize_copy method of the class.
Prints obj on the given port (default $>). Equivalent to:
def display(port=$>)
port.write self
end
For example:
1.display "cat".display [ 4, 5, 6 ].display puts
produces:
1cat456
Produces a shallow copy of obj—the instance variables of obj are copied, but not the objects they reference. dup copies the tainted state of obj. See also the discussion under Object#clone. In general, clone and dup may have different semantics in descendent classes. While clone is used to duplicate an object, including its internal state, dup typically uses the class of the descendent object to create the new instance.
This method may have class-specific behavior. If so, that behavior will be documented under the #initialize_copy method of the class.
Returns Enumerable::Enumerator.new(self, method, *args).
e.g.:
str = "xyz"
enum = str.enum_for(:each_byte)
a = enum.map {|b| '%02x' % b } #=> ["78", "79", "7a"]
# protects an array from being modified
a = [1, 2, 3]
some_method(a.to_enum)
Equality—At the Object level, == returns true only if obj and other are the same object. Typically, this method is overridden in descendent classes to provide class-specific meaning.
Unlike ==, the equal? method should never be overridden by subclasses: it is used to determine object identity (that is, a.equal?(b) iff a is the same object as b).
The eql? method returns true if obj and anObject have the same value. Used by Hash to test members for equality. For objects of class Object, eql? is synonymous with ==. Subclasses normally continue this tradition, but there are exceptions. Numeric types, for example, perform type conversion across ==, but not across eql?, so:
1 == 1.0 #=> true 1.eql? 1.0 #=> false
Equality—At the Object level, == returns true only if obj and other are the same object. Typically, this method is overridden in descendent classes to provide class-specific meaning.
Unlike ==, the equal? method should never be overridden by subclasses: it is used to determine object identity (that is, a.equal?(b) iff a is the same object as b).
The eql? method returns true if obj and anObject have the same value. Used by Hash to test members for equality. For objects of class Object, eql? is synonymous with ==. Subclasses normally continue this tradition, but there are exceptions. Numeric types, for example, perform type conversion across ==, but not across eql?, so:
1 == 1.0 #=> true 1.eql? 1.0 #=> false
Adds to obj the instance methods from each module given as a parameter.
module Mod
def hello
"Hello from Mod.\n"
end
end
class Klass
def hello
"Hello from Klass.\n"
end
end
k = Klass.new
k.hello #=> "Hello from Klass.\n"
k.extend(Mod) #=> #<Klass:0x401b3bc8>
k.hello #=> "Hello from Mod.\n"
Prevents further modifications to obj. A TypeError will be raised if modification is attempted. There is no way to unfreeze a frozen object. See also Object#frozen?.
a = [ "a", "b", "c" ] a.freeze a << "z"
produces:
prog.rb:3:in `<<': can't modify frozen array (TypeError)
from prog.rb:3
Returns the freeze status of obj.
a = [ "a", "b", "c" ] a.freeze #=> ["a", "b", "c"] a.frozen? #=> true
Evaluates a string containing Ruby source code, or the given block, within the context of the receiver (obj). In order to set the context, the variable self is set to obj while the code is executing, giving the code access to obj‘s instance variables. In the version of instance_eval that takes a String, the optional second and third parameters supply a filename and starting line number that are used when reporting compilation errors.
class Klass
def initialize
@secret = 99
end
end
k = Klass.new
k.instance_eval { @secret } #=> 99
Executes the given block within the context of the receiver (obj). In order to set the context, the variable self is set to obj while the code is executing, giving the code access to obj‘s instance variables. Arguments are passed as block parameters.
class KlassWithSecret
def initialize
@secret = 99
end
end
k = KlassWithSecret.new
k.instance_exec(5) {|x| @secret+x } #=> 104
Returns true if obj is an instance of the given class. See also Object#kind_of?.
Returns true if the given instance variable is defined in obj.
class Fred
def initialize(p1, p2)
@a, @b = p1, p2
end
end
fred = Fred.new('cat', 99)
fred.instance_variable_defined?(:@a) #=> true
fred.instance_variable_defined?("@b") #=> true
fred.instance_variable_defined?("@c") #=> false
Returns the value of the given instance variable, or nil if the instance variable is not set. The @ part of the variable name should be included for regular instance variables. Throws a NameError exception if the supplied symbol is not valid as an instance variable name.
class Fred
def initialize(p1, p2)
@a, @b = p1, p2
end
end
fred = Fred.new('cat', 99)
fred.instance_variable_get(:@a) #=> "cat"
fred.instance_variable_get("@b") #=> 99
Sets the instance variable names by symbol to object, thereby frustrating the efforts of the class‘s author to attempt to provide proper encapsulation. The variable did not have to exist prior to this call.
class Fred
def initialize(p1, p2)
@a, @b = p1, p2
end
end
fred = Fred.new('cat', 99)
fred.instance_variable_set(:@a, 'dog') #=> "dog"
fred.instance_variable_set(:@c, 'cat') #=> "cat"
fred.inspect #=> "#<Fred:0x401b3da8 @a=\"dog\", @b=99, @c=\"cat\">"
Returns an array of instance variable names for the receiver. Note that simply defining an accessor does not create the corresponding instance variable.
class Fred
attr_accessor :a1
def initialize
@iv = 3
end
end
Fred.new.instance_variables #=> ["@iv"]
Returns true if class is the class of obj, or if class is one of the superclasses of obj or modules included in obj.
module M; end
class A
include M
end
class B < A; end
class C < B; end
b = B.new
b.instance_of? A #=> false
b.instance_of? B #=> true
b.instance_of? C #=> false
b.instance_of? M #=> false
b.kind_of? A #=> true
b.kind_of? B #=> true
b.kind_of? C #=> false
b.kind_of? M #=> true
Returns true if class is the class of obj, or if class is one of the superclasses of obj or modules included in obj.
module M; end
class A
include M
end
class B < A; end
class C < B; end
b = B.new
b.instance_of? A #=> false
b.instance_of? B #=> true
b.instance_of? C #=> false
b.instance_of? M #=> false
b.kind_of? A #=> true
b.kind_of? B #=> true
b.kind_of? C #=> false
b.kind_of? M #=> true
Looks up the named method as a receiver in obj, returning a Method object (or raising NameError). The Method object acts as a closure in obj‘s object instance, so instance variables and the value of self remain available.
class Demo
def initialize(n)
@iv = n
end
def hello()
"Hello, @iv = #{@iv}"
end
end
k = Demo.new(99)
m = k.method(:hello)
m.call #=> "Hello, @iv = 99"
l = Demo.new('Fred')
m = l.method("hello")
m.call #=> "Hello, @iv = Fred"
Returns a list of the names of methods publicly accessible in obj. This will include all the methods accessible in obj‘s ancestors.
class Klass
def kMethod()
end
end
k = Klass.new
k.methods[0..9] #=> ["kMethod", "freeze", "nil?", "is_a?",
"class", "instance_variable_set",
"methods", "extend", "__send__", "instance_eval"]
k.methods.length #=> 42
Returns an integer identifier for obj. The same number will be returned on all calls to id for a given object, and no two active objects will share an id. Object#object_id is a different concept from the :name notation, which returns the symbol id of name. Replaces the deprecated Object#id.
Removes the named instance variable from obj, returning that variable‘s value.
class Dummy
attr_reader :var
def initialize
@var = 99
end
def remove
remove_instance_variable(:@var)
end
end
d = Dummy.new
d.var #=> 99
d.remove #=> 99
d.var #=> nil
Invoked as a callback whenever a singleton method is added to the receiver.
module Chatty
def Chatty.singleton_method_added(id)
puts "Adding #{id.id2name}"
end
def self.one() end
def two() end
def Chatty.three() end
end
produces:
Adding singleton_method_added Adding one Adding three
Invoked as a callback whenever a singleton method is removed from the receiver.
module Chatty
def Chatty.singleton_method_removed(id)
puts "Removing #{id.id2name}"
end
def self.one() end
def two() end
def Chatty.three() end
class <<self
remove_method :three
remove_method :one
end
end
produces:
Removing three Removing one
Invoked as a callback whenever a singleton method is undefined in the receiver.
module Chatty
def Chatty.singleton_method_undefined(id)
puts "Undefining #{id.id2name}"
end
def Chatty.one() end
class << self
undef_method(:one)
end
end
produces:
Undefining one
Returns an array of the names of singleton methods for obj. If the optional all parameter is true, the list will include methods in modules included in obj.
module Other
def three() end
end
class Single
def Single.four() end
end
a = Single.new
def a.one()
end
class << a
include Other
def two()
end
end
Single.singleton_methods #=> ["four"]
a.singleton_methods(false) #=> ["two", "one"]
a.singleton_methods #=> ["two", "one", "three"]
Marks obj as tainted—if the $SAFE level is set appropriately, many method calls which might alter the running programs environment will refuse to accept tainted strings.
Yields x to the block, and then returns x. The primary purpose of this method is to "tap into" a method chain, in order to perform operations on intermediate results within the chain.
(1..10).tap {
|x| puts "original: #{x.inspect}"
}.to_a.tap {
|x| puts "array: #{x.inspect}"
}.select {|x| x%2==0}.tap {
|x| puts "evens: #{x.inspect}"
}.map {|x| x*x}.tap {
|x| puts "squares: #{x.inspect}"
}
Returns an array representation of obj. For objects of class Object and others that don‘t explicitly override the method, the return value is an array containing self. However, this latter behavior will soon be obsolete.
self.to_a #=> -:1: warning: default `to_a' will be obsolete "hello".to_a #=> ["hello"] Time.new.to_a #=> [39, 54, 8, 9, 4, 2003, 3, 99, true, "CDT"]
Returns Enumerable::Enumerator.new(self, method, *args).
e.g.:
str = "xyz"
enum = str.enum_for(:each_byte)
a = enum.map {|b| '%02x' % b } #=> ["78", "79", "7a"]
# protects an array from being modified
a = [1, 2, 3]
some_method(a.to_enum)