ruby - 为什么不能在 `singleton` `Fixnum` ,`Bignum` ,`Float` 类对象上定义 ,`Symbol` 方法，但 ` FalseClass` 和 `TrueClass` 可以有？

Question

为什么不能在Fixnum,Bignum,Float,上定义singleton方法Symbol类对象，但是FalseClass和TrueClass可以有吗？

C:\>ruby -v
ruby 2.0.0p0 (2013-02-24) [i386-mingw32]

C:\>irb --simple-prompt
DL is deprecated, please use Fiddle
11111111111.class
#=> Bignum
class << 11111111111 ; end
#TypeError: can't define singleton
#        from (irb):2
#        from C:/Ruby200/bin/irb:12:in `<main>'

1111.class
#=> Fixnum
class << 1111 ; end
#TypeError: can't define singleton
#       from (irb):4
#       from C:/Ruby200/bin/irb:12:in `<main>'

11.11.class
#=> Float
class << 11.11 ; end
#TypeError: can't define singleton
#       from (irb):6
#       from C:/Ruby200/bin/irb:12:in `<main>'

:name.class
#=> Symbol
class << :name ; end
#TypeError: can't define singleton
#       from (irb):8
#       from C:/Ruby200/bin/irb:12:in `<main>'

Answer 1

作为Ruby Docs说:

There is effectively only one Fixnum object instance for any given integer value, so, for example, you cannot add a singleton method to a Fixnum.

Bignum、Float 和 Symbol 也是如此