2011-12-06 20:05:31 +00:00
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require 'set'
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module Docile
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2013-07-28 20:42:30 +00:00
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# A proxy object with a primary receiver as well as a secondary
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# fallback receiver.
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#
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# Will attempt to forward all method calls first to the primary receiver,
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# and then to the fallback receiver if the primary does not handle that
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# method.
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2011-12-06 20:05:31 +00:00
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class FallbackContextProxy
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2013-07-28 20:42:30 +00:00
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# The set of methods which will **not** be proxied, but instead answered
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# by this object directly.
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2013-07-25 14:02:05 +00:00
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NON_PROXIED_METHODS = Set[:__send__, :object_id, :__id__, :==, :equal?,
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:"!", :"!=", :instance_exec, :instance_variables,
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:instance_variable_get, :instance_variable_set,
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2011-12-06 21:21:11 +00:00
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:remove_instance_variable]
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2013-07-28 20:42:30 +00:00
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# The set of instance variables which are local to this object and hidden.
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# All other instance variables will be copied in and out of this object
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# from the scope in which this proxy was created.
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2011-12-06 21:21:11 +00:00
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NON_PROXIED_INSTANCE_VARIABLES = Set[:@__receiver__, :@__fallback__]
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2011-12-06 20:05:31 +00:00
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2013-07-28 20:42:30 +00:00
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# Undefine all instance methods except those in {NON_PROXIED_METHODS}
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2011-12-06 20:05:31 +00:00
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instance_methods.each do |method|
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2013-07-25 14:03:04 +00:00
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undef_method(method) unless NON_PROXIED_METHODS.include?(method.to_sym)
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2011-12-06 20:05:31 +00:00
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end
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2013-07-28 20:42:30 +00:00
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# @param [Object] receiver the primary proxy target to which all methods
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# initially will be forwarded
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# @param [Object] fallback the fallback proxy target to which any methods
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# not handled by `receiver` will be forwarded
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2011-12-06 20:05:31 +00:00
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def initialize(receiver, fallback)
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@__receiver__ = receiver
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@__fallback__ = fallback
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end
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2013-07-28 20:42:30 +00:00
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# @return [Array<Symbol>] Instance variable names, excluding
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# {NON_PROXIED_INSTANCE_VARIABLES}
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#
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# @note on Ruby 1.8.x, the instance variable names are actually of
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# type `String`.
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2011-12-06 21:21:11 +00:00
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def instance_variables
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2013-07-24 20:20:50 +00:00
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# Ruby 1.8.x returns string names, convert to symbols for compatibility
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super.select { |v| !NON_PROXIED_INSTANCE_VARIABLES.include?(v.to_sym) }
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2011-12-06 21:21:11 +00:00
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end
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2013-07-28 20:42:30 +00:00
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# Proxy all methods, excluding {NON_PROXIED_METHODS}, first to `receiver`
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# and then to `fallback` if not found.
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2011-12-06 20:05:31 +00:00
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def method_missing(method, *args, &block)
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2013-07-25 14:03:04 +00:00
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@__receiver__.__send__(method.to_sym, *args, &block)
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rescue ::NoMethodError => e
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@__fallback__.__send__(method.to_sym, *args, &block)
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2011-12-06 20:05:31 +00:00
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end
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end
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2013-04-01 03:27:12 +00:00
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end
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