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

Object#instance_variable_set

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.

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\">"

Object#remove_instance_variable

Removes the named instance variable from obj, returning that variable’s value. String arguments are converted to symbols.

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

Enumerator#each_with_index

Same as Enumerator#with_index(0), i.e. there is no starting offset.

If no block is given, a new Enumerator is returned that includes the index.

Module#public_instance_methods

Returns a list of the public instance methods defined in mod. If the optional parameter is false, the methods of any ancestors are not included.

Module#protected_instance_methods

Returns a list of the protected instance methods defined in mod. If the optional parameter is false, the methods of any ancestors are not included.

Module#private_instance_methods

Returns a list of the private instance methods defined in mod. If the optional parameter is false, the methods of any ancestors are not included.

module Mod
  def method1()  end
  private :method1
  def method2()  end
end
Mod.instance_methods           #=> [:method2]
Mod.private_instance_methods   #=> [:method1]

Module#class_variable_defined?

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

class Fred
  @@foo = 99
end
Fred.class_variable_defined?(:@@foo)    #=> true
Fred.class_variable_defined?(:@@bar)    #=> false

Module#public_instance_method

Similar to instance_method, searches public method only.

Module#public_method_defined?

Returns true if the named public method is defined by mod. If inherit is set, the lookup will also search mod’s ancestors. String arguments are converted to symbols.

module A
  def method1()  end
end
class B
  protected
  def method2()  end
end
class C < B
  include A
  def method3()  end
end

A.method_defined? :method1                 #=> true
C.public_method_defined? "method1"         #=> true
C.public_method_defined? "method1", true   #=> true
C.public_method_defined? "method1", false  #=> true
C.public_method_defined? "method2"         #=> false
C.method_defined? "method2"                #=> true

Module#private_method_defined?

Returns true if the named private method is defined by mod. If inherit is set, the lookup will also search mod’s ancestors. String arguments are converted to symbols.

module A
  def method1()  end
end
class B
  private
  def method2()  end
end
class C < B
  include A
  def method3()  end
end

A.method_defined? :method1                   #=> true
C.private_method_defined? "method1"          #=> false
C.private_method_defined? "method2"          #=> true
C.private_method_defined? "method2", true    #=> true
C.private_method_defined? "method2", false   #=> false
C.method_defined? "method2"                  #=> false

Module#protected_method_defined?

Returns true if the named protected method is defined mod. If inherit is set, the lookup will also search mod’s ancestors. String arguments are converted to symbols.

module A
  def method1()  end
end
class B
  protected
  def method2()  end
end
class C < B
  include A
  def method3()  end
end

A.method_defined? :method1                    #=> true
C.protected_method_defined? "method1"         #=> false
C.protected_method_defined? "method2"         #=> true
C.protected_method_defined? "method2", true   #=> true
C.protected_method_defined? "method2", false  #=> false
C.method_defined? "method2"                   #=> true

BigDecimal::save_rounding_mode

Execute the provided block, but preserve the rounding mode

BigDecimal.save_rounding_mode do
  BigDecimal.mode(BigDecimal::ROUND_MODE, :up)
  puts BigDecimal.mode(BigDecimal::ROUND_MODE)
end

For use with the BigDecimal::ROUND_*

See BigDecimal.mode