How do you tell the Rails version inside of a Rails app?

Up to R开发者_高级运维ails 2.3.8, there is a constant:

RAILS_GEM_VERSION   "2.3.8"

but Rails 3.0.0 doesn't have it. Is there other ways?

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Use Rails.version.

Most environment information that you might need from Rails should be accessible from that class.

The documentation.