63 lines
2.3 KiB
Ruby
63 lines
2.3 KiB
Ruby
module ActiveSupport
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module CachingTools #:nodoc:
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# Provide shortcuts to simply the creation of nested default hashes. This
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# pattern is useful, common practice, and unsightly when done manually.
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module HashCaching
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# Dynamically create a nested hash structure used to cache calls to +method_name+
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# The cache method is named +#{method_name}_cache+ unless :as => :alternate_name
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# is given.
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#
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# The hash structure is created using nested Hash.new. For example:
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#
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# def slow_method(a, b) a ** b end
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#
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# can be cached using hash_cache :slow_method, which will define the method
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# slow_method_cache. We can then find the result of a ** b using:
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#
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# slow_method_cache[a][b]
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#
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# The hash structure returned by slow_method_cache would look like this:
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#
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# Hash.new do |as, a|
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# as[a] = Hash.new do |bs, b|
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# bs[b] = slow_method(a, b)
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# end
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# end
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#
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# The generated code is actually compressed onto a single line to maintain
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# sensible backtrace signatures.
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#
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def hash_cache(method_name, options = {})
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selector = options[:as] || "#{method_name}_cache"
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method = self.instance_method(method_name)
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args = []
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code = "def #{selector}(); @#{selector} ||= "
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(1..method.arity).each do |n|
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args << "v#{n}"
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code << "Hash.new {|h#{n}, v#{n}| h#{n}[v#{n}] = "
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end
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# Add the method call with arguments, followed by closing braces and end.
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code << "#{method_name}(#{args * ', '}) #{'}' * method.arity} end"
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# Extract the line number information from the caller. Exceptions arising
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# in the generated code should point to the +hash_cache :...+ line.
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if caller[0] && /^(.*):(\d+)$/ =~ caller[0]
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file, line_number = $1, $2.to_i
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else # We can't give good trackback info; fallback to this line:
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file, line_number = __FILE__, __LINE__
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end
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# We use eval rather than building proc's because it allows us to avoid
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# linking the Hash's to this method's binding. Experience has shown that
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# doing so can cause obtuse memory leaks.
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class_eval code, file, line_number
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end
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end
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end
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end
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