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const_missing 

        # Module.const_missing

(from ruby core)
---
    mod.const_missing(sym)    -> obj

---

Invoked when a reference is made to an undefined constant in *mod*. It
is passed a symbol for the undefined constant, and returns a value to be
used for that constant. The following code is an example of the same:

    def Foo.const_missing(name)
      name # return the constant name as Symbol
    end

    Foo::UNDEFINED_CONST    #=> :UNDEFINED_CONST: symbol returned

In the next example when a reference is made to an undefined constant,
it attempts to load a file whose name is the lowercase version of the
constant (thus class `Fred` is assumed to be in file `fred.rb`).  If
found, it returns the loaded class. It therefore implements an autoload
feature similar to Kernel#autoload and Module#autoload.

    def Object.const_missing(name)
      @looked_for ||= {}
      str_name = name.to_s
      raise "Class not found: #{name}" if @looked_for[str_name]
      @looked_for[str_name] = 1
      file = str_name.downcase
      require file
      klass = const_get(name)
      return klass if klass
      raise "Class not found: #{name}"
    end

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