Is it allowed to write code without method enclosure in a class / module? what does this code mean? [closed]

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For example a file in acti开发者_运维知识库ve_support/core_ext/exception.rb

it started with:

module ActiveSupport
  if RUBY_VERSION >= '1.9'
    FrozenObjectError = RuntimeError
  else
    FrozenObjectError = TypeError
  end
end

Then continued with class Exception code

what does it mean? What do you use FrozenObjectError, RuntimeError, and TypeError objects for? How do I know where they are initialized? why do we need these lines of code?

Could you recommend me a good book to learn about this, please?

Thanks

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Yes -- every line in Ruby is within an object, even the global scope. For your example, the 'error' for violating a Frozen Object is set based on what version is being run. In 1.9 it's a runtime exception whereas prior is a type error (this has to do with changes introduced in 1.9). This makes the exception as descriptive as possible.

Programming Ruby is very elegant at explaining the language:

Programming Ruby