The JSON gem adds a few modules to Ruby core classes containing :to_json definition, overwriting their default behavior. That said, we need to define the basic to_json method in all of them, otherwise they will always use to_json gem implementation, which is backwards incompatible in several cases (for instance, the JSON implementation for Hash does not work) with inheritance and consequently classes as ActiveSupport::OrderedHash cannot be serialized to json.

On the other hand, we should avoid conflict with ::JSON.{generate,dump}(obj). Unfortunately, the JSON gem's encoder relies on its own to_json implementation to encode objects. Since it always passes a ::JSON::State object as the only argument to to_json, we can detect that and forward the calls to the original to_json method.

It should be noted that when using ::JSON.{generate,dump} directly, ActiveSupport's encoder is bypassed completely. This means that as_json won't be invoked and the JSON gem will simply ignore any options it does not natively understand. This also means that ::JSON.{generate,dump} should give exactly the same results with or without active support.

Namespace
Methods
G
V
Class Public methods
gem_version()

Returns the version of the currently loaded Active Support as a Gem::Version.

# File activesupport/lib/active_support/gem_version.rb, line 3
def self.gem_version
  Gem::Version.new VERSION::STRING
end
version()

Returns the version of the currently loaded ActiveSupport as a Gem::Version

# File activesupport/lib/active_support/version.rb, line 5
def self.version
  gem_version
end