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Object
Douglas G. Allen edited this page Jan 15, 2015
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=begin
Object
Object is the default root of all Ruby objects.
Object inherits from BasicObject
which allows creating alternate object hierarchies.
Methods on Object are available to all classes 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.
When referencing constants in classes inheriting from Object you do not need
to use the full namespace.
For example,
referencing File inside YourClass will find the top-level File class.
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).
Constants
ARGF
ARGF is a stream designed for use in scripts that process
files given as command-line arguments or passed in via STDIN.
See ARGF (the class) for more details.
ARGV
ARGV contains the command line arguments used to run ruby
with the first value containing the name of the executable.
A library like OptionParser can be used to process command-line arguments.
DATA
DATA is a File that contains the data section of the executed file.
To create a data section use __END__:
$ cat t.rb
puts DATA.gets
__END__
hello world!
$ ruby t.rb
hello world!
ENV
ENV is a Hash-like accessor for environment variables.
See ENV (the class) for more details.
FALSE
An alias of false
NIL
An alias of nil
RUBY_COPYRIGHT
The copyright string for ruby
RUBY_DESCRIPTION
The full ruby version string, like ruby -v prints’
RUBY_ENGINE
The engine or interpreter this ruby uses.
RUBY_PATCHLEVEL
The patchlevel for this ruby.
If this is a development build of ruby the patchlevel will be -1
RUBY_PLATFORM
The platform for this ruby
RUBY_RELEASE_DATE
The date this ruby was released
RUBY_REVISION
The SVN revision for this ruby.
RUBY_VERSION
The running version of ruby
STDERR
Holds the original stderr
STDIN
Holds the original stdin
STDOUT
Holds the original stdout
TOPLEVEL_BINDING
The Binding of the top level scope
TRUE
An alias of true
Public Instance Methods
obj !~ other → true or false
Returns true if two objects do not match (using the =~ method),
otherwise false.
obj <=> other → 0 or nil
Returns 0 if obj and other are the same object or obj == other,
otherwise nil.
The <=> is used by various methods to compare objects,
for example Enumerable#sort, Enumerable#max etc.
Your implementation of <=> should return
one of the following values: -1, 0, 1 or nil.
-1 means self is smaller than other. 0 means self is equal to other.
1 means self is bigger than other.
Nil means the two values could not be compared.
When you define <=>,
you can include Comparable to gain the methods <=, <, ==, >=, > and between?.
obj === other → true or false
Case Equality – For class Object,
effectively the same as calling #==,
but typically overridden by descendants
to provide meaningful semantics in case statements.
obj =~ other → nil
Pattern Match—Overridden by descendants
(notably Regexp and String) to provide meaningful pattern-match semantics.
class → class
Returns the class of obj.
This method must always be called with an explicit receiver,
as class is also a reserved word in Ruby.
=end
1.class #=> Fixnum
self.class #=> Object
=begin
clone → an_object
Produces a shallow copy of obj—the instance variables of obj are copied,
but not the objects they reference.
clone copies the frozen and tainted state of obj.
See also the discussion under Object#dup.
=end
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\">"
=begin
This method may have class-specific behavior.
If so, that behavior will be documented under the
#initialize_copy method of the class.
define_singleton_method(symbol, method) → new_method
define_singleton_method(symbol) { block } → proc
Defines a singleton method in the receiver.
The method parameter can be a Proc,
a Method or an UnboundMethod object.
If a block is specified, it is used as the method body.
=end
class A
class << self
def class_name
to_s
end
end
end
A.define_singleton_method(:who_am_i) do
"I am: #{class_name}"
end
A.who_am_i # ==> "I am: A"
guy = "Bob"
guy.define_singleton_method(:hello) { "#{self}: Hello there!" }
guy.hello #=> "Bob: Hello there!"
=begin
display(port=$>) → nil
Prints obj on the given port (default $>). Equivalent to:
=end
def display(port=$>)
port.write self
end
# For example:
1.display
"cat".display
[ 4, 5, 6 ].display
puts
# produces:
1cat456
=begin
dup → an_object
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.
This method may have class-specific behavior.
If so, that behavior will be documented under the
#initialize_copy method of the class.
on dup vs clone¶ ↑
In general,
clone and dup may have different semantics in descendant classes.
While clone is used to duplicate an object,
including its internal state,
dup typically uses the class of the descendant object to
create the new instance.
When using dup,
any modules that the object has been extended with will not be copied.
=end
class Klass
attr_accessor :str
end
module Foo
def foo; 'foo'; end
end
s1 = Klass.new #=> #<Klass:0x401b3a38>
s1.extend(Foo) #=> #<Klass:0x401b3a38>
s1.foo #=> "foo"
s2 = s1.clone #=> #<Klass:0x401b3a38>
s2.foo #=> "foo"
s3 = s1.dup #=> #<Klass:0x401b3a38>
s3.foo #=> NoMethodError: undefined method `foo' for #<Klass:0x401b3a38>
=begin
enum_for(method = :each, *args) → enum
enum_for(method = :each, *args){|*args| block} → enum
Creates a new Enumerator which will enumerate by calling method on obj,
passing args if any.
If a block is given,
it will be used to calculate the size of the enumerator without the need
to iterate it
(see Enumerator#size).
Examples¶ ↑
=end
str = "xyz"
enum = str.enum_for(:each_byte)
enum.each { |b| puts b }
# => 120
# => 121
# => 122
# protect an array from being modified by some_method
a = [1, 2, 3]
some_method(a.to_enum)
=begin
It is typical to call #to_enum when defining methods for a generic
Enumerable,
in case no block is passed.
Here is such an example,
with parameter passing and a sizing block:
=end
module Enumerable
# a generic method to repeat the values of any enumerable
def repeat(n)
raise ArgumentError, "#{n} is negative!" if n < 0
unless block_given?
return to_enum(__method__, n) do # __method__ is :repeat here
sz = size # Call size and multiply by n...
sz * n if sz # but return nil if size itself is nil
end
end
each do |*val|
n.times { yield *val }
end
end
end
%[hello world].repeat(2) { |w| puts w }
# => Prints 'hello', 'hello', 'world', 'world'
enum = (1..14).repeat(3)
# => returns an Enumerator when called without a block
enum.first(4) # => [1, 1, 1, 2]
enum.size # => 42
=begin
obj == other → true or false
equal?(other) → true or false
eql?(other) → true or false
Equality — At the Object level,
== returns true only if obj and other are the same object.
Typically,
this method is overridden in descendant classes to provide
class-specific meaning.
Unlike ==,
the equal?
method should never be overridden by subclasses as it is used to
determine object identity
(that is, a.equal?(b) if and only if a is the same object as b):
=end
obj = "a"
other = obj.dup
obj == other #=> true
obj.equal? other #=> false
obj.equal? obj #=> true
=begin
The eql? method returns true if obj and other refer to the same hash key.
This is used by Hash to test members for equality.
For objects of class Object, eql? is synonymous with ==.
Subclasses normally continue this tradition by aliasing eql? to their
overridden == method,
but there are exceptions. Numeric types,
for example, perform type conversion across ==,
but not across eql?, so:
=end
1 == 1.0 #=> true
1.eql? 1.0 #=> false
=begin
extend(module, ...) → obj
Adds to obj the instance methods from each module given as a parameter.
=end
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"
=begin
freeze → obj
Prevents further modifications to obj.
A RuntimeError will be raised if modification is attempted.
There is no way to unfreeze a frozen object. See also Object#frozen?.
This method returns self.
=end
a = [ "a", "b", "c" ]
a.freeze
a << "z"
# produces:
#=> prog.rb:3:in `<<': can't modify frozen Array (RuntimeError)
# from prog.rb:3
=begin
Objects of the following classes are always frozen:
Fixnum, Bignum, Float, Symbol.
frozen? → true or false
Returns the freeze status of obj.
=end
a = [ "a", "b", "c" ]
a.freeze #=> ["a", "b", "c"]
a.frozen? #=> true
=begin
hash → fixnum
Generates a Fixnum hash value for this object.
This function must have the property that a.eql?(b) implies a.hash == b.hash.
The hash value is used along with eql?
by the Hash class to determine if two objects reference the same hash key.
Any hash value that exceeds the capacity of a Fixnum will be
truncated before being used.
The hash value for an object may not be identical across invocations or
implementations of Ruby.
If you need a stable identifier across Ruby invocations and implementations
you will need to generate one with a custom method.
inspect → string
Returns a string containing a human-readable representation of obj.
The default inspect shows the object’s class name,
an encoding of the object id,
and a list of the instance variables and their values
(by calling inspect on each of them).
User defined classes should override this method to provide a
better representation of obj.
When overriding this method,
it should return a string whose encoding is compatible with the
default external encoding.
=end
[ 1, 2, 3..4, 'five' ].inspect #=> "[1, 2, 3..4, \"five\"]"
Time.new.inspect #=> "2008-03-08 19:43:39 +0900"
class Foo
end
Foo.new.inspect #=> "#<Foo:0x0300c868>"
class Bar
def initialize
@bar = 1
end
end
Bar.new.inspect #=> "#<Bar:0x0300c868 @bar=1>"
=begin
instance_of?(class) → true or false
Returns true if obj is an instance of the given class.
See also Object#kind_of?.
=end
class A; 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
=begin
instance_variable_defined?(symbol) → true or false
instance_variable_defined?(string) → true or false
Returns true if the given instance variable is defined in obj.
String arguments are converted to symbols.
=end
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
=begin
instance_variable_get(symbol) → obj
instance_variable_get(string) → obj
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.
String arguments are converted to symbols.
=end
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
=begin
instance_variable_set(symbol, obj) → obj
instance_variable_set(string, obj) → obj
Sets the instance variable named by symbol to the given object,
thereby frustrating the efforts of the class’s author to attempt
to provide proper encapsulation.
The variable does not have to exist prior to this call.
If the instance variable name is passed as a string,
that string is converted to a symbol.
=end
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\">"
=begin
instance_variables → array
Returns an array of instance variable names for the receiver.
Note that simply defining an accessor does not
create the corresponding instance variable.
=end
class Fred
attr_accessor :a1
def initialize
@iv = 3
end
end
Fred.new.instance_variables #=> [:@iv]
=begin
is_a?(class) → true or false
Returns true if class is the class of obj,
or if class is one of the superclasses of obj or modules included in obj.
=end
module M; end
class A
include M
end
class B < A; end
class C < B; end
b = B.new
b.is_a? A #=> true
b.is_a? B #=> true
b.is_a? C #=> false
b.is_a? M #=> true
b.kind_of? A #=> true
b.kind_of? B #=> true
b.kind_of? C #=> false
b.kind_of? M #=> true
=begin
itself → an_object
Returns obj.
=end
string = 'my string' #=> "my string"
string.itself.object_id == string.object_id #=> true
=begin
kind_of?(class) → true or false
Returns true if class is the class of obj,
or if class is one of the superclasses of obj or modules included in obj.
=end
module M; end
class A
include M
end
class B < A; end
class C < B; end
b = B.new
b.is_a? A #=> true
b.is_a? B #=> true
b.is_a? C #=> false
b.is_a? M #=> true
b.kind_of? A #=> true
b.kind_of? B #=> true
b.kind_of? C #=> false
b.kind_of? M #=> true
=begin
method(sym) → method
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.
=end
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"
=begin
methods(regular=true) → array
Returns a list of the names of public and protected methods of obj.
This will include all the methods accessible in obj’s ancestors.
If the optional parameter is false,
it returns an array of obj<i>‘s public and protected singleton methods,
the array will not include methods in modules included in <i>obj.
=end
class Klass
def klass_method()
end
end
k = Klass.new
k.methods[0..9] #=> [:klass_method, :nil?, :===,
# :==~, :!, :eql?
# :hash, :<=>, :class, :singleton_class]
k.methods.length #=> 56
k.methods(false) #=> []
def k.singleton_method; end
k.methods(false) #=> [:singleton_method]
module M123; def m123; end end
k.extend M123
k.methods(false) #=> [:singleton_method]
=begin
nil? → true or false
Only the object nil responds true to nil?.
=end
Object.new.nil? #=> false
nil.nil? #=> true
=begin
__id__ → integer
object_id → integer
Returns an integer identifier for obj.
The same number will be returned on all calls to object_id for a
given object,
and no two active objects will share an id.
Note: that some objects of builtin classes are reused for optimization.
This is the case for immediate values and frozen string literals.
Immediate values are not passed by reference but are passed by value:
nil, true, false, Fixnums, Symbols, and some Floats.
=end
Object.new.object_id == Object.new.object_id # => false
(21 * 2).object_id == (21 * 2).object_id # => true
"hello".object_id == "hello".object_id # => false
"hi".freeze.object_id == "hi".freeze.object_id # => true
=begin
private_methods(all=true) → array
Returns the list of private methods accessible to obj.
If the all parameter is set to false,
only those methods in the receiver will be listed.
protected_methods(all=true) → array
Returns the list of protected methods accessible to obj.
If the all parameter is set to false,
only those methods in the receiver will be listed.
public_method(sym) → method
Similar to method, searches public method only.
public_methods(all=true) → array
Returns the list of public methods accessible to obj.
If the all parameter is set to false,
only those methods in the receiver will be listed.
public_send(symbol [, args...]) → obj
public_send(string [, args...]) → obj
Invokes the method identified by symbol,
passing it any arguments specified.
Unlike send,
#public_send calls public methods only.
When the method is identified by a string,
the string is converted to a symbol.
=end
1.public_send(:puts, "hello") # causes NoMethodError
=begin
remove_instance_variable(symbol) → obj
Removes the named instance variable from obj,
returning that variable’s value.
=end
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
=begin
respond_to?(symbol, include_all=false) → true or false
respond_to?(string, include_all=false) → true or false
Returns true if obj responds to the given method.
Private and protected methods are included in the search only if
the optional second parameter evaluates to true.
If the method is not implemented,
as Process.fork on Windows,
File.lchmod on GNU/Linux, etc., false is returned.
If the method is not defined,
respond_to_missing?
method is called and the result is returned.
When the method name parameter is given as a string,
the string is converted to a symbol.
respond_to_missing?(symbol, include_all) → true or false
respond_to_missing?(string, include_all) → true or false
DO NOT USE THIS DIRECTLY.
Hook method to return whether the obj can respond to id method or not.
When the method name parameter is given as a string,
the string is converted to a symbol.
See respond_to?, and the example of BasicObject.
send(symbol [, args...]) → obj
__send__(symbol [, args...]) → obj
send(string [, args...]) → obj
__send__(string [, args...]) → obj
Invokes the method identified by symbol,
passing it any arguments specified.
You can use __send__ if the name send clashes with an existing method in obj.
When the method is identified by a string,
the string is converted to a symbol.
=end
class Klass
def hello(*args)
"Hello " + args.join(' ')
end
end
k = Klass.new
k.send :hello, "gentle", "readers" #=> "Hello gentle readers"
=begin
singleton_class → class
Returns the singleton class of obj.
This method creates a new singleton class if obj does not have one.
If obj is nil, true, or false,
it returns NilClass, TrueClass, or FalseClass, respectively.
If obj is a Fixnum or a Symbol, it raises a TypeError.
=end
Object.new.singleton_class #=> #<Class:#<Object:0xb7ce1e24>>
String.singleton_class #=> #<Class:String>
nil.singleton_class #=> NilClass
=begin
singleton_method(sym) → method
Similar to method, searches singleton method only.
=end
class Demo
def initialize(n)
@iv = n
end
def hello()
"Hello, @iv = #{@iv}"
end
end
k = Demo.new(99)
def k.hi
"Hi, @iv = #{@iv}"
end
m = k.singleton_method(:hi)
m.call #=> "Hi, @iv = 99"
m = k.singleton_method(:hello) #=> NameError
=begin
singleton_methods(all=true) → array
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.
Only public and protected singleton methods are returned.
=end
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]
=begin
taint → obj
Mark the object as tainted.
Objects that are marked as tainted will be restricted from
various built-in methods.
This is to prevent insecure data,
such as command-line arguments or strings read from Kernel#gets,
from inadvertently compromising the user’s system.
To check whether an object is tainted, use tainted?.
You should only untaint a tainted object if your code has
inspected it and
determined that it is safe.
To do so use untaint.
In $SAFE level 3,
all newly created objects are tainted and you can’t untaint objects.
tainted? → true or false
Returns true if the object is tainted.
See taint for more information.
tap{|x|...} → obj
Yields self to the block, and then returns self.
The primary purpose of this method is to “tap into” a method chain,
in order to perform operations on intermediate results within the chain.
=end
(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}"}
=begin
to_enum(method = :each, *args) → enum
to_enum(method = :each, *args) {|*args| block} → enum
Creates a new Enumerator which will enumerate by calling method on obj,
passing args if any.
If a block is given,
it will be used to calculate the size of the enumerator without the
need to iterate it
(see Enumerator#size).
Examples¶ ↑
=end
str = "xyz"
enum = str.enum_for(:each_byte)
enum.each { |b| puts b }
# => 120
# => 121
# => 122
# protect an array from being modified by some_method
a = [1, 2, 3]
some_method(a.to_enum)
=begin
It is typical to call #to_enum when defining methods for a
generic Enumerable,
in case no block is passed.
Here is such an example, with parameter passing and a sizing block:
=end
module Enumerable
# a generic method to repeat the values of any enumerable
def repeat(n)
raise ArgumentError, "#{n} is negative!" if n < 0
unless block_given?
return to_enum(__method__, n) do # __method__ is :repeat here
sz = size # Call size and multiply by n...
sz * n if sz # but return nil if size itself is nil
end
end
each do |*val|
n.times { yield *val }
end
end
end
%[hello world].repeat(2) { |w| puts w }
# => Prints 'hello', 'hello', 'world', 'world'
enum = (1..14).repeat(3)
# => returns an Enumerator when called without a block
enum.first(4) # => [1, 1, 1, 2]
enum.size # => 42
=begin
to_s → string
Returns a string representing obj.
The default to_s prints the object’s class and an encoding of the
object id.
As a special case,
the top-level object that is the initial execution context of
Ruby programs returns “main”.
trust → obj
Deprecated method that is equivalent to untaint.
untaint → obj
Removes the tainted mark from the object.
See taint for more information.
untrust → obj
Deprecated method that is equivalent to taint.
untrusted? → true or false
Deprecated method that is equivalent to tainted?.
=end