In Rails, how are validators, for example “validates_numericality_of” implemented?

1) validates_numericality_of is one of many validations that exists in the Rails framework, or ActiveRecord to be more precise. So it is not something that is accesible for all Ruby classes. You use it be passing ruby symbols that represents attributes for the model.

You can pass several attributes at the same time.

Validates_numericality_of validates whether the value of the specified attribute is numeric.

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