class Object - RDoc Documentation

# class 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`).

## What’s Here¶ ↑

First, what’s elsewhere. Class Object:

- Inherits from class BasicObject.

- Includes module Kernel.

Here, class Object provides methods for:

- Querying

- Instance Variables

- Other

### Querying¶ ↑

- #!~: Returns `true` if `self` does not match the given object, otherwise `false`.

- #<=>: Returns 0 if `self` and the given object `object` are the same object, or if `self == object`; otherwise returns `nil`.

- `===`: Implements case equality, effectively the same as calling `==`.

- `eql?`: Implements hash equality, effectively the same as calling `==`.

- `kind_of?` (aliased as `is_a?`): Returns whether given argument is an ancestor of the singleton class of `self`.

- `instance_of?`: Returns whether `self` is an instance of the given class.

- `instance_variable_defined?`: Returns whether the given instance variable is defined in `self`.

- `method`: Returns the `Method` object for the given method in `self`.

- `methods`: Returns an array of symbol names of public and protected methods in `self`.

- `nil?`: Returns `false`. (Only `nil` responds `true` to method `nil?`.)

- `object_id`: Returns an integer corresponding to `self` that is unique for the current process

- `private_methods`: Returns an array of the symbol names of the private methods in `self`.

- `protected_methods`: Returns an array of the symbol names of the protected methods in `self`.

- `public_method`: Returns the `Method` object for the given public method in `self`.

- `public_methods`: Returns an array of the symbol names of the public methods in `self`.

- `respond_to?`: Returns whether `self` responds to the given method.

- `singleton_class`: Returns the singleton class of `self`.

- `singleton_method`: Returns the `Method` object for the given singleton method in `self`.

- `singleton_methods`: Returns an array of the symbol names of the singleton methods in `self`.

- `define_singleton_method`: Defines a singleton method in `self` for the given symbol method-name and block or proc.

- `extend`: Includes the given modules in the singleton class of `self`.

- `public_send`: Calls the given public method in `self` with the given argument.

- `send`: Calls the given method in `self` with the given argument.

### Instance Variables¶ ↑

- `instance_variable_get`: Returns the value of the given instance variable in `self`, or `nil` if the instance variable is not set.

- `instance_variable_set`: Sets the value of the given instance variable in `self` to the given object.

- `instance_variables`: Returns an array of the symbol names of the instance variables in `self`.

- `remove_instance_variable`: Removes the named instance variable from `self`.

### Other¶ ↑

- `clone`: Returns a shallow copy of `self`, including singleton class and frozen state.

- `define_singleton_method`: Defines a singleton method in `self` for the given symbol method-name and block or proc.

- `display`: Prints `self` to the given `IO` stream or `$stdout`.

- `dup`: Returns a shallow unfrozen copy of `self`.

- `enum_for` (aliased as `to_enum`): Returns an `Enumerator` for `self` using the using the given method, arguments, and block.

- `extend`: Includes the given modules in the singleton class of `self`.

- `freeze`: Prevents further modifications to `self`.

- `hash`: Returns the integer hash value for `self`.

- `inspect`: Returns a human-readable string representation of `self`.

- `itself`: Returns `self`.

- `method_missing`: `Method` called when an undefined method is called on `self`.

- `public_send`: Calls the given public method in `self` with the given argument.

- `send`: Calls the given method in `self` with the given argument.

- `to_s`: Returns a string representation of `self`.

### 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.

  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.

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_ENGINE_VERSION

  The version of 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 GIT commit hash 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

### Public Instance Methods

obj !~ other → true or false click to toggle source

Returns true if two objects do not match (using the =~ method), otherwise false.

    static VALUE
    rb_obj_not_match(VALUE obj1, VALUE obj2)
    {
        VALUE result = rb_funcall(obj1, id_match, 1, obj2);
        return rb_obj_not(result);
    }

obj <=> other → 0 or nil click to toggle source

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?.

    static VALUE
    rb_obj_cmp(VALUE obj1, VALUE obj2)
    {
        if (rb_equal(obj1, obj2))
            return INT2FIX(0);
        return Qnil;
    }

true === other → true or false click to toggle source
false === other → true or false
nil === other → true or false

Returns `true` or `false`.

Like `Object#==`, if `object` is an instance of `Object` (and not an instance of one of its many subclasses).

This method is commonly overridden by those subclasses, to provide meaningful semantics in `case` statements.

    #define case_equal rb_equal

define_singleton_method(symbol, method) → symbol click to toggle source
define_singleton_method(symbol) { block } → symbol

Defines a public 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. If a block or a method has parameters, they’re used as method parameters.

    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!"

    chris = "Chris"
    chris.define_singleton_method(:greet) {|greeting| "#{greeting}, I'm Chris!" }
    chris.greet("Hi") #=> "Hi, I'm Chris!"

    static VALUE
    rb_obj_define_method(int argc, VALUE *argv, VALUE obj)
    {
        VALUE klass = rb_singleton_class(obj);
        const rb_scope_visibility_t scope_visi = {METHOD_VISI_PUBLIC, FALSE};

        return rb_mod_define_method_with_visibility(argc, argv, klass, &scope_visi);
    }

display(port = $>) → nil click to toggle source

Writes `self` on the given port:

    1.display
    "cat".display
    [ 4, 5, 6 ].display
    puts

Output:

    1cat[4, 5, 6]

    static VALUE
    rb_obj_display(int argc, VALUE *argv, VALUE self)
    {
        VALUE out;

        out = (!rb_check_arity(argc, 0, 1) ? rb_ractor_stdout() : argv[0]);
        rb_io_write(out, self);

        return Qnil;
    }

dup → an_object click to toggle source

Produces a shallow copy of obj—the instance variables of obj are copied, but not the objects they reference.

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.

    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:0x401be280>
    s2.foo #=> "foo"

    s3 = s1.dup #=> #<Klass:0x401c1084>
    s3.foo #=> NoMethodError: undefined method `foo' for #<Klass:0x401c1084>

    VALUE
    rb_obj_dup(VALUE obj)
    {
        VALUE dup;

        if (special_object_p(obj)) {
            return obj;
        }
        dup = rb_obj_alloc(rb_obj_class(obj));
        return rb_obj_dup_setup(obj, dup);
    }

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. What was yielded by method becomes values of enumerator.

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¶ ↑

    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)

    # String#split in block form is more memory-effective:
    very_large_string.split("|") { |chunk| return chunk if chunk.include?('DATE') }
    # This could be rewritten more idiomatically with to_enum:
    very_large_string.to_enum(:split, "|").lazy.grep(/DATE/).first

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:

    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

    %i[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

Alias for: to_enum
obj == other → true or false click to toggle source
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`):

    obj = "a"
    other = obj.dup

    obj == other      #=> true
    obj.equal? other  #=> false
    obj.equal? obj    #=> true

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 any pair of objects where `eql?` returns `true`, the `hash` value of both objects must be equal. So any subclass that overrides `eql?` should also override `hash` appropriately.

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:

    1 == 1.0     #=> true
    1.eql? 1.0   #=> false

    VALUE
    rb_obj_equal(VALUE obj1, VALUE obj2)
    {
        return RBOOL(obj1 == obj2);
    }

extend(module, ...) → obj click to toggle source

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"

    static VALUE
    rb_obj_extend(int argc, VALUE *argv, VALUE obj)
    {
        int i;
        ID id_extend_object, id_extended;

        CONST_ID(id_extend_object, "extend_object");
        CONST_ID(id_extended, "extended");

        rb_check_arity(argc, 1, UNLIMITED_ARGUMENTS);
        for (i = 0; i < argc; i++) {
            Check_Type(argv[i], T_MODULE);
            if (FL_TEST(argv[i], RMODULE_IS_REFINEMENT)) {
                rb_raise(rb_eTypeError, "Cannot extend object with refinement");
            }
        }
        while (argc--) {
            rb_funcall(argv[argc], id_extend_object, 1, obj);
            rb_funcall(argv[argc], id_extended, 1, obj);
        }
        return obj;
    }

freeze → obj click to toggle source

Prevents further modifications to obj. A `FrozenError` will be raised if modification is attempted. There is no way to unfreeze a frozen object. See also `Object#frozen?`.

This method returns self.

    a = [ "a", "b", "c" ]
    a.freeze
    a << "z"

produces:

    prog.rb:3:in `<<': can't modify frozen Array (FrozenError)
     from prog.rb:3

Objects of the following classes are always frozen: `Integer`, `Float`, `Symbol`.

    VALUE
    rb_obj_freeze(VALUE obj)
    {
        if (!OBJ_FROZEN(obj)) {
            OBJ_FREEZE(obj);
            if (SPECIAL_CONST_P(obj)) {
                rb_bug("special consts should be frozen.");
            }
        }
        return obj;
    }

hash → integer click to toggle source

Generates an `Integer` 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 an `Integer` 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.

Certain core classes such as `Integer` use built-in hash calculations and do not call the `hash` method when used as a hash key.

When implementing your own `hash` based on multiple values, the best practice is to combine the class and any values using the hash code of an array:

For example:

    def hash
      [self.class, a, b, c].hash
    end

The reason for this is that the `Array#hash` method already has logic for safely and efficiently combining multiple hash values.

    VALUE
    rb_obj_hash(VALUE obj)
    {
        long hnum = any_hash(obj, objid_hash);
        return ST2FIX(hnum);
    }

inspect → string click to toggle source

Returns a string containing a human-readable representation of obj. The default `inspect` shows the object’s class name, an encoding of its memory address, 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.

    [ 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>"

    static VALUE
    rb_obj_inspect(VALUE obj)
    {
        if (rb_ivar_count(obj) > 0) {
            VALUE str;
            VALUE c = rb_class_name(CLASS_OF(obj));

            str = rb_sprintf("-<%"PRIsVALUE":%p", c, (void*)obj);
            return rb_exec_recursive(inspect_obj, obj, str);
        }
        else {
            return rb_any_to_s(obj);
        }
    }

instance_of?(class) → true or false click to toggle source

Returns `true` if obj is an instance of the given class. See also `Object#kind_of?`.

    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

    VALUE
    rb_obj_is_instance_of(VALUE obj, VALUE c)
    {
        c = class_or_module_required(c);
        return RBOOL(rb_obj_class(obj) == c);
    }

instance_variable_defined?(symbol) → true or false click to toggle source
instance_variable_defined?(string) → true or false

Returns `true` if the given instance variable is defined in obj. `String` arguments are converted to symbols.

    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

    static VALUE
    rb_obj_ivar_defined(VALUE obj, VALUE iv)
    {
        ID id = id_for_var(obj, iv, instance);

        if (!id) {
            return Qfalse;
        }
        return rb_ivar_defined(obj, id);
    }

instance_variable_get(symbol) → obj click to toggle source
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.

    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

    static VALUE
    rb_obj_ivar_get(VALUE obj, VALUE iv)
    {
        ID id = id_for_var(obj, iv, instance);

        if (!id) {
            return Qnil;
        }
        return rb_ivar_get(obj, id);
    }

instance_variable_set(symbol, obj) → obj click to toggle source
instance_variable_set(string, obj) → obj

Sets the instance variable named by symbol to the given object. This may circumvent the encapsulation intended by the author of the class, so it should be used with care. 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.

    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\">"

    static VALUE
    rb_obj_ivar_set_m(VALUE obj, VALUE iv, VALUE val)
    {
        ID id = id_for_var(obj, iv, instance);
        if (!id) id = rb_intern_str(iv);
        return rb_ivar_set(obj, id, val);
    }

instance_variables → array click to toggle source

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]

    VALUE
    rb_obj_instance_variables(VALUE obj)
    {
        VALUE ary;

        ary = rb_ary_new();
        rb_ivar_foreach(obj, ivar_i, ary);
        return ary;
    }

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.

    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

Alias for: kind_of?
itself → obj click to toggle source

Returns the receiver.

    string = "my string"
    string.itself.object_id == string.object_id   #=> true

    static VALUE
    rb_obj_itself(VALUE obj)
    {
        return obj;
    }

kind_of?(class) → true or false click to toggle source

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.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

    VALUE
    rb_obj_is_kind_of(VALUE obj, VALUE c)
    {
        VALUE cl = CLASS_OF(obj);

        RUBY_ASSERT(RB_TYPE_P(cl, T_CLASS));

        // Fastest path: If the object's class is an exact match we know `c` is a
        // class without checking type and can return immediately.
        if (cl == c) return Qtrue;

        // Note: YJIT needs this function to never allocate and never raise when
        // `c` is a class or a module.

        if (LIKELY(RB_TYPE_P(c, T_CLASS))) {
            // Fast path: Both are T_CLASS
            return class_search_class_ancestor(cl, c);
        }
        else if (RB_TYPE_P(c, T_ICLASS)) {
            // First check if we inherit the includer
            // If we do we can return true immediately
            VALUE includer = RCLASS_INCLUDER(c);
            if (cl == includer) return Qtrue;

            // Usually includer is a T_CLASS here, except when including into an
            // already included Module.
            // If it is a class, attempt the fast class-to-class check and return
            // true if there is a match.
            if (RB_TYPE_P(includer, T_CLASS) && class_search_class_ancestor(cl, includer))
                return Qtrue;

            // We don't include the ICLASS directly, so must check if we inherit
            // the module via another include
            return RBOOL(class_search_ancestor(cl, RCLASS_ORIGIN(c)));
        }
        else if (RB_TYPE_P(c, T_MODULE)) {
            // Slow path: check each ancestor in the linked list and its method table
            return RBOOL(class_search_ancestor(cl, RCLASS_ORIGIN(c)));
        }
        else {
            rb_raise(rb_eTypeError, "class or module required");
            UNREACHABLE_RETURN(Qfalse);
        }
    }

Also aliased as: is_a?
method(sym) → method click to toggle source

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"

Note that `Method` implements `to_proc` method, which means it can be used with iterators.

    [ 1, 2, 3 ].each(&method(:puts)) # => prints 3 lines to stdout

    out = File.open('test.txt', 'w')
    [ 1, 2, 3 ].each(&out.method(:puts)) # => prints 3 lines to file

    require 'date'
    %w[2017-03-01 2017-03-02].collect(&Date.method(:parse))
    #=> [#<Date: 2017-03-01 ((2457814j,0s,0n),+0s,2299161j)>, #<Date: 2017-03-02 ((2457815j,0s,0n),+0s,2299161j)>]

    VALUE
    rb_obj_method(VALUE obj, VALUE vid)
    {
        return obj_method(obj, vid, FALSE);
    }

methods(regular=true) → array click to toggle source

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’s public and protected singleton methods, the array will not include methods in modules included in obj.

    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]

    VALUE
    rb_obj_methods(int argc, const VALUE *argv, VALUE obj)
    {
        rb_check_arity(argc, 0, 1);
        if (argc > 0 && !RTEST(argv[0])) {
            return rb_obj_singleton_methods(argc, argv, obj);
        }
        return class_instance_method_list(argc, argv, CLASS_OF(obj), 1, ins_methods_i);
    }

nil? → true or false click to toggle source

Only the object nil responds `true` to `nil?`.

    Object.new.nil?   #=> false
    nil.nil?          #=> true

    VALUE
    rb_false(VALUE obj)
    {
        return Qfalse;
    }

__id__ → integer click to toggle source
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.

`BasicObject` implements +__id__+, `Kernel` implements `object_id`.

Immediate values are not passed by reference but are passed by value: `nil`, `true`, `false`, Fixnums, Symbols, and some Floats.

    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

    VALUE
    rb_obj_id(VALUE obj)
    {
        /* If obj is an immediate, the object ID is obj directly converted to a Numeric.
         * Otherwise, the object ID is a Numeric that is a non-zero multiple of
         * (RUBY_IMMEDIATE_MASK + 1) which guarantees that it does not collide with
         * any immediates. */
        return rb_find_object_id(rb_gc_get_objspace(), obj, rb_gc_impl_object_id);
    }

private_methods(all=true) → array click to toggle source

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.

    VALUE
    rb_obj_private_methods(int argc, const VALUE *argv, VALUE obj)
    {
        return class_instance_method_list(argc, argv, CLASS_OF(obj), 1, ins_methods_priv_i);
    }

protected_methods(all=true) → array click to toggle source

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.

    VALUE
    rb_obj_protected_methods(int argc, const VALUE *argv, VALUE obj)
    {
        return class_instance_method_list(argc, argv, CLASS_OF(obj), 1, ins_methods_prot_i);
    }

public_method(sym) → method click to toggle source

Similar to method, searches public method only.

    VALUE
    rb_obj_public_method(VALUE obj, VALUE vid)
    {
        return obj_method(obj, vid, TRUE);
    }

public_methods(all=true) → array click to toggle source

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.

    VALUE
    rb_obj_public_methods(int argc, const VALUE *argv, VALUE obj)
    {
        return class_instance_method_list(argc, argv, CLASS_OF(obj), 1, ins_methods_pub_i);
    }

public_send(symbol [, args...]) → obj click to toggle source
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.

    1.public_send(:puts, "hello")  # causes NoMethodError

    static VALUE
    rb_f_public_send(int argc, VALUE *argv, VALUE recv)
    {
        return send_internal_kw(argc, argv, recv, CALL_PUBLIC);
    }

remove_instance_variable(symbol) → obj click to toggle source
remove_instance_variable(string) → obj

Removes the named instance variable from obj, returning that variable’s value. The name can be passed as a symbol or as a string.

    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

    VALUE
    rb_obj_remove_instance_variable(VALUE obj, VALUE name)
    {
        const ID id = id_for_var(obj, name, an, instance);

        // Frozen check comes here because it's expected that we raise a
        // NameError (from the id_for_var check) before we raise a FrozenError
        rb_check_frozen(obj);

        if (id) {
            VALUE val = rb_ivar_delete(obj, id, Qundef);

            if (!UNDEF_P(val)) return val;
        }

        rb_name_err_raise("instance variable %1$s not defined",
                          obj, name);
        UNREACHABLE_RETURN(Qnil);
    }

respond_to?(symbol, include_all=false) → true or false click to toggle source
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.

    static VALUE
    obj_respond_to(int argc, VALUE *argv, VALUE obj)
    {
        VALUE mid, priv;
        ID id;
        rb_execution_context_t *ec = GET_EC();

        rb_scan_args(argc, argv, "11", &mid, &priv);
        if (!(id = rb_check_id(&mid))) {
            VALUE ret = basic_obj_respond_to_missing(ec, CLASS_OF(obj), obj,
                                                     rb_to_symbol(mid), priv);
            if (UNDEF_P(ret)) ret = Qfalse;
            return ret;
        }
        return  RBOOL(basic_obj_respond_to(ec, obj, id, !RTEST(priv)));
    }

respond_to_missing?(symbol, include_all) → true or false click to toggle source
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`.

    static VALUE
    obj_respond_to_missing(VALUE obj, VALUE mid, VALUE priv)
    {
        return Qfalse;
    }

send(symbol [, args...]) → obj click to toggle source
__send__(symbol [, args...]) → obj
send(string [, args...]) → obj
__send__(string [, args...]) → obj

Invokes the method identified by symbol, passing it any arguments specified. When the method is identified by a string, the string is converted to a symbol.

`BasicObject` implements +__send__+, `Kernel` implements `send`. `__send__` is safer than `send` when obj has the same method name like `Socket`. See also `public_send`.

    class Klass
      def hello(*args)
        "Hello " + args.join(' ')
      end
    end
    k = Klass.new
    k.send :hello, "gentle", "readers"   #=> "Hello gentle readers"

    VALUE
    rb_f_send(int argc, VALUE *argv, VALUE recv)
    {
        return send_internal_kw(argc, argv, recv, CALL_FCALL);
    }

singleton_class → class click to toggle source

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 an `Integer`, a `Float` or a `Symbol`, it raises a `TypeError`.

    Object.new.singleton_class  #=> #<Class:#<Object:0xb7ce1e24>>
    String.singleton_class      #=> #<Class:String>
    nil.singleton_class         #=> NilClass

    static VALUE
    rb_obj_singleton_class(VALUE obj)
    {
        return rb_singleton_class(obj);
    }

singleton_method(sym) → method click to toggle source

Similar to method, searches singleton method only.

    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

    VALUE
    rb_obj_singleton_method(VALUE obj, VALUE vid)
    {
        VALUE sc = rb_singleton_class_get(obj);
        VALUE klass;
        ID id = rb_check_id(&vid);

        if (NIL_P(sc) ||
            NIL_P(klass = RCLASS_ORIGIN(sc)) ||
            !NIL_P(rb_special_singleton_class(obj))) {
            /* goto undef; */
        }
        else if (! id) {
            VALUE m = mnew_missing_by_name(klass, obj, &vid, FALSE, rb_cMethod);
            if (m) return m;
            /* else goto undef; */
        }
        else {
            VALUE args[2] = {obj, vid};
            VALUE ruby_method = rb_rescue(rb_obj_singleton_method_lookup, (VALUE)args, rb_obj_singleton_method_lookup_fail, Qfalse);
            if (ruby_method) {
                struct METHOD *method = (struct METHOD *)RTYPEDDATA_GET_DATA(ruby_method);
                VALUE lookup_class = RBASIC_CLASS(obj);
                VALUE stop_class = rb_class_superclass(sc);
                VALUE method_class = method->iclass;

                /* Determine if method is in singleton class, or module included in or prepended to it */
                do {
                    if (lookup_class == method_class) {
                        return ruby_method;
                    }
                    lookup_class = RCLASS_SUPER(lookup_class);
                } while (lookup_class && lookup_class != stop_class);
            }
        }

      /* undef: */
        vid = ID2SYM(id);
        rb_name_err_raise("undefined singleton method '%1$s' for '%2$s'",
                          obj, vid);
        UNREACHABLE_RETURN(Qundef);
    }

singleton_methods(all=true) → array click to toggle source

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.

    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]

    VALUE
    rb_obj_singleton_methods(int argc, const VALUE *argv, VALUE obj)
    {
        VALUE ary, klass, origin;
        struct method_entry_arg me_arg;
        struct rb_id_table *mtbl;
        int recur = TRUE;

        if (rb_check_arity(argc, 0, 1)) recur = RTEST(argv[0]);
        if (RCLASS_SINGLETON_P(obj)) {
            rb_singleton_class(obj);
        }
        klass = CLASS_OF(obj);
        origin = RCLASS_ORIGIN(klass);
        me_arg.list = st_init_numtable();
        me_arg.recur = recur;
        if (klass && RCLASS_SINGLETON_P(klass)) {
            if ((mtbl = RCLASS_M_TBL(origin)) != 0) rb_id_table_foreach(mtbl, method_entry_i, &me_arg);
            klass = RCLASS_SUPER(klass);
        }
        if (recur) {
            while (klass && (RCLASS_SINGLETON_P(klass) || RB_TYPE_P(klass, T_ICLASS))) {
                if (klass != origin && (mtbl = RCLASS_M_TBL(klass)) != 0) rb_id_table_foreach(mtbl, method_entry_i, &me_arg);
                klass = RCLASS_SUPER(klass);
            }
        }
        ary = rb_ary_new2(me_arg.list->num_entries);
        st_foreach(me_arg.list, ins_methods_i, ary);
        st_free_table(me_arg.list);

        return ary;
    }

to_enum(method = :each, *args) → enum click to toggle source
to_enum(method = :each, *args) {|*args| block} → enum

Creates a new `Enumerator` which will enumerate by calling `method` on `obj`, passing `args` if any. What was yielded by method becomes values of enumerator.

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¶ ↑

    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)

    # String#split in block form is more memory-effective:
    very_large_string.split("|") { |chunk| return chunk if chunk.include?('DATE') }
    # This could be rewritten more idiomatically with to_enum:
    very_large_string.to_enum(:split, "|").lazy.grep(/DATE/).first

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:

    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

    %i[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

    static VALUE
    obj_to_enum(int argc, VALUE *argv, VALUE obj)
    {
        VALUE enumerator, meth = sym_each;

        if (argc > 0) {
            --argc;
            meth = *argv++;
        }
        enumerator = rb_enumeratorize_with_size(obj, meth, argc, argv, 0);
        if (rb_block_given_p()) {
            RB_OBJ_WRITE(enumerator, &enumerator_ptr(enumerator)->size, rb_block_proc());
        }
        return enumerator;
    }

Also aliased as: enum_for
to_s → string click to toggle source

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”.

    VALUE
    rb_any_to_s(VALUE obj)
    {
        VALUE str;
        VALUE cname = rb_class_name(CLASS_OF(obj));

        str = rb_sprintf("#<%"PRIsVALUE":%p>", cname, (void*)obj);

        return str;
    }