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.

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