class BasicObject - Documentation for Ruby 3.3

# class BasicObject

`BasicObject` is the parent class of all classes in Ruby. It’s an explicit blank class.

`BasicObject` can be used for creating object hierarchies independent of Ruby’s object hierarchy, proxy objects like the `Delegator` class, or other uses where namespace pollution from Ruby’s methods and classes must be avoided.

To avoid polluting `BasicObject` for other users an appropriately named subclass of `BasicObject` should be created instead of directly modifying BasicObject:

    class MyObjectSystem < BasicObject
    end

`BasicObject` does not include `Kernel` (for methods like `puts`) and `BasicObject` is outside of the namespace of the standard library so common classes will not be found without using a full class path.

A variety of strategies can be used to provide useful portions of the standard library to subclasses of `BasicObject`. A subclass could `include Kernel` to obtain `puts`, `exit`, etc. A custom Kernel-like module could be created and included or delegation can be used via `method_missing`:

    class MyObjectSystem < BasicObject
      DELEGATE = [:puts, :p]

      def method_missing(name, *args, &block)
        return super unless DELEGATE.include? name
        ::Kernel.send(name, *args, &block)
      end

      def respond_to_missing?(name, include_private = false)
        DELEGATE.include?(name) or super
      end
    end

Access to classes and modules from the Ruby standard library can be obtained in a `BasicObject` subclass by referencing the desired constant from the root like `::File` or `::Enumerator`. Like `method_missing`, const_missing can be used to delegate constant lookup to `Object`:

    class MyObjectSystem < BasicObject
      def self.const_missing(name)
        ::Object.const_get(name)
      end
    end

### What’s Here¶ ↑

These are the methods defined for BasicObject:

- `::new`: Returns a new BasicObject instance.

- `!`: Returns the boolean negation of `self`: `true` or `false`.

- `!=`: Returns whether `self` and the given object are not equal.

- `==`: Returns whether `self` and the given object are equivalent.

- `__id__`: Returns the integer object identifier for `self`.

- `__send__`: Calls the method identified by the given symbol.

- `equal?`: Returns whether `self` and the given object are the same object.

- `instance_eval`: Evaluates the given string or block in the context of `self`.

- `instance_exec`: Executes the given block in the context of `self`, passing the given arguments.

### Public Class Methods

new click to toggle source

Returns a new `BasicObject`.

    #define rb_obj_initialize rb_obj_dummy0

### Public Instance Methods

!obj → true or false click to toggle source

Boolean negate.

    VALUE
    rb_obj_not(VALUE obj)
    {
        return RBOOL(!RTEST(obj));
    }

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

Returns true if two objects are not-equal, otherwise false.

    VALUE
    rb_obj_not_equal(VALUE obj1, VALUE obj2)
    {
        VALUE result = rb_funcall(obj1, id_eq, 1, obj2);
        return rb_obj_not(result);
    }

obj == other → true or false click to toggle source
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);
    }

Also aliased as: equal?
__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)
    {
        /*
         *                32-bit VALUE space
         *          MSB ------------------------ LSB
         *  false   00000000000000000000000000000000
         *  true    00000000000000000000000000000010
         *  nil     00000000000000000000000000000100
         *  undef   00000000000000000000000000000110
         *  symbol  ssssssssssssssssssssssss00001110
         *  object  oooooooooooooooooooooooooooooo00        = 0 (mod sizeof(RVALUE))
         *  fixnum  fffffffffffffffffffffffffffffff1
         *
         *                    object_id space
         *                                       LSB
         *  false   00000000000000000000000000000000
         *  true    00000000000000000000000000000010
         *  nil     00000000000000000000000000000100
         *  undef   00000000000000000000000000000110
         *  symbol   000SSSSSSSSSSSSSSSSSSSSSSSSSSS0        S...S % A = 4 (S...S = s...s * A + 4)
         *  object   oooooooooooooooooooooooooooooo0        o...o % A = 0
         *  fixnum  fffffffffffffffffffffffffffffff1        bignum if required
         *
         *  where A = sizeof(RVALUE)/4
         *
         *  sizeof(RVALUE) is
         *  20 if 32-bit, double is 4-byte aligned
         *  24 if 32-bit, double is 8-byte aligned
         *  40 if 64-bit
         */

        return rb_find_object_id(obj, cached_object_id);
    }

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);
    }

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

Alias for: ==
instance_eval(string [, filename [, lineno]] ) → obj click to toggle source
instance_eval {|obj| block } → obj

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 and private methods.

When `instance_eval` is given a block, obj is also passed in as the block’s only argument.

When `instance_eval` is given a `String`, the optional second and third parameters supply a filename and starting line number that are used when reporting compilation errors.

    class KlassWithSecret
      def initialize
        @secret = 99
      end
      private
      def the_secret
        "Ssssh! The secret is #{@secret}."
      end
    end
    k = KlassWithSecret.new
    k.instance_eval { @secret }          #=> 99
    k.instance_eval { the_secret }       #=> "Ssssh! The secret is 99."
    k.instance_eval {|obj| obj == self } #=> true

    static VALUE
    rb_obj_instance_eval_internal(int argc, const VALUE *argv, VALUE self)
    {
        return specific_eval(argc, argv, self, TRUE, RB_PASS_CALLED_KEYWORDS);
    }

instance_exec(arg...) {|var...| block } → obj click to toggle source

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

    static VALUE
    rb_obj_instance_exec_internal(int argc, const VALUE *argv, VALUE self)
    {
        return yield_under(self, TRUE, argc, argv, RB_PASS_CALLED_KEYWORDS);
    }

### Private Instance Methods

method_missing(symbol [, *args] ) → result click to toggle source

Invoked by Ruby when obj is sent a message it cannot handle. symbol is the symbol for the method called, and args are any arguments that were passed to it. By default, the interpreter raises an error when this method is called. However, it is possible to override the method to provide more dynamic behavior. If it is decided that a particular method should not be handled, then super should be called, so that ancestors can pick up the missing method. The example below creates a class `Roman`, which responds to methods with names consisting of roman numerals, returning the corresponding integer values.

    class Roman
      def roman_to_int(str)
        # ...
      end

      def method_missing(symbol, *args)
        str = symbol.id2name
        begin
          roman_to_int(str)
        rescue
          super(symbol, *args)
        end
      end
    end

    r = Roman.new
    r.iv      #=> 4
    r.xxiii   #=> 23
    r.mm      #=> 2000
    r.foo     #=> NoMethodError

    static VALUE
    rb_method_missing(int argc, const VALUE *argv, VALUE obj)
    {
        rb_execution_context_t *ec = GET_EC();
        raise_method_missing(ec, argc, argv, obj, ec->method_missing_reason);
        UNREACHABLE_RETURN(Qnil);
    }

singleton_method_added(symbol) click to toggle source

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

    #define rb_obj_singleton_method_added rb_obj_dummy1

singleton_method_removed(symbol) click to toggle source

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

    #define rb_obj_singleton_method_removed rb_obj_dummy1

singleton_method_undefined(symbol) click to toggle source

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

    #define rb_obj_singleton_method_undefined rb_obj_dummy1