When writing my plugin Spreadsheet Architect I needed to check if methods were defined on both the class and instances. Heres two fast ways to do this:

Post.respond_to?(:item_name) #=> false
@post.respond_to?(:item_name) #=> true

# Check if the instance method is defined
Post.method_defined?(:some_instance_method) #=> false
@post.method_defined?(:some_instance_method) #=> true

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• Stack Overflow - given-a-class-see-if-instance-has-method-ruby