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module Arel
module Visitors
class Visitor
def accept object
visit object
end
private
DISPATCH = Hash.new do |hash, visitor_class|
hash[visitor_class] =
Hash.new do |method_hash, node_class|
method_hash[node_class] = "visit_#{(node_class.name || '').gsub('::', '_')}"
end
end
def dispatch
DISPATCH[self.class]
end
def visit object
send dispatch[object.class], object
rescue NoMethodError => e
raise e if respond_to?(dispatch[object.class], true)
superklass = object.class.ancestors.find { |klass|
respond_to?(dispatch[klass], true)
}
raise(TypeError, "Cannot visit #{object.class}") unless superklass
dispatch[object.class] = dispatch[superklass]
retry
end
end
end
end
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