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module Arel
module Visitors
class Visitor
def initialize
@dispatch = get_dispatch_cache
end
def accept object
visit object
end
private
def self.dispatch_cache
dispatch = Hash.new do |hash, class_name|
hash[class_name] = "visit_#{(class_name || '').gsub('::', '_')}"
end
# pre-populate cache. FIXME: this should be passed in to each
# instance, but we can do that later.
self.class.private_instance_methods.sort.each do |name|
next unless name =~ /^visit_(.*)$/
dispatch[$1.gsub('_', '::')] = name
end
dispatch
end
def get_dispatch_cache
self.class.dispatch_cache
end
def dispatch
@dispatch
end
def visit object
send dispatch[object.class.name], object
rescue NoMethodError => e
raise e if respond_to?(dispatch[object.class.name], true)
superklass = object.class.ancestors.find { |klass|
respond_to?(dispatch[klass.name], true)
}
raise(TypeError, "Cannot visit #{object.class}") unless superklass
dispatch[object.class.name] = dispatch[superklass.name]
retry
end
end
end
end
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