146 lines
3.5 KiB
Ruby
146 lines
3.5 KiB
Ruby
# encoding: utf-8
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module Memoizable
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# Build the memoized method
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class MethodBuilder
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# Raised when the method arity is invalid
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class InvalidArityError < ArgumentError
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# Initialize an invalid arity exception
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#
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# @param [Module] descendant
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# @param [Symbol] method
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# @param [Integer] arity
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#
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# @api private
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def initialize(descendant, method, arity)
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super("Cannot memoize #{descendant}##{method}, its arity is #{arity}")
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end
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end # InvalidArityError
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# Raised when a block is passed to a memoized method
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class BlockNotAllowedError < ArgumentError
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# Initialize a block not allowed exception
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#
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# @param [Module] descendant
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# @param [Symbol] method
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#
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# @api private
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def initialize(descendant, method)
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super("Cannot pass a block to #{descendant}##{method}, it is memoized")
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end
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end # BlockNotAllowedError
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# The original method before memoization
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#
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# @return [UnboundMethod]
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#
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# @api public
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attr_reader :original_method
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# Initialize an object to build a memoized method
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#
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# @param [Module] descendant
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# @param [Symbol] method_name
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# @param [#call] freezer
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#
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# @return [undefined]
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#
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# @api private
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def initialize(descendant, method_name, freezer)
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@descendant = descendant
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@method_name = method_name
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@freezer = freezer
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@original_visibility = visibility
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@original_method = @descendant.instance_method(@method_name)
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assert_arity(@original_method.arity)
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end
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# Build a new memoized method
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#
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# @example
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# method_builder.call # => creates new method
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#
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# @return [MethodBuilder]
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#
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# @api public
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def call
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remove_original_method
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create_memoized_method
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set_method_visibility
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self
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end
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private
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# Assert the method arity is zero
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#
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# @param [Integer] arity
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#
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# @return [undefined]
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#
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# @raise [InvalidArityError]
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#
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# @api private
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def assert_arity(arity)
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if arity.nonzero?
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fail InvalidArityError.new(@descendant, @method_name, arity)
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end
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end
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# Remove the original method
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#
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# @return [undefined]
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#
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# @api private
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def remove_original_method
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name = @method_name
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@descendant.module_eval { undef_method(name) }
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end
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# Create a new memoized method
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#
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# @return [undefined]
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#
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# @api private
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def create_memoized_method
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name, method, freezer = @method_name, @original_method, @freezer
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@descendant.module_eval do
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define_method(name) do |&block|
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fail BlockNotAllowedError.new(self.class, name) if block
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memoized_method_cache.fetch(name) do
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freezer.call(method.bind(self).call)
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end
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end
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end
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end
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# Set the memoized method visibility to match the original method
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#
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# @return [undefined]
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#
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# @api private
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def set_method_visibility
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@descendant.send(@original_visibility, @method_name)
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end
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# Get the visibility of the original method
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#
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# @return [Symbol]
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#
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# @api private
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def visibility
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if @descendant.private_method_defined?(@method_name) then :private
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elsif @descendant.protected_method_defined?(@method_name) then :protected
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else :public
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end
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end
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end # MethodBuilder
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end # Memoizable
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