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Add CachingTools::HashCaching to simplify the creation of nested, aut…

…ofilling hashes.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4059 5ecf4fe2-1ee6-0310-87b1-e25e094e27de
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commit 24403498ba8582d29f55aab16ffd5920dec1c669 1 parent 3f496c6
@seckar seckar authored
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2  activesupport/CHANGELOG
@@ -1,5 +1,7 @@
*SVN*
+* Add CachingTools::HashCaching to simplify the creation of nested, autofilling hashes. [Nicholas Seckar]
+
* Remove a hack intended to avoid unloading the same class twice, but which would not work anyways. [Nicholas Seckar]
* Update Object.subclasses_of to locate nested classes. This affects Object.remove_subclasses_of in that nested classes will now be unloaded. [Nicholas Seckar]
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62 activesupport/lib/active_support/caching_tools.rb
@@ -0,0 +1,62 @@
+module ActiveSupport
+ module CachingTools #:nodoc:
+
+ # Provide shortcuts to simply the creation of nested default hashes. This
+ # pattern is useful, common practice, and unsightly when done manually.
+ module HashCaching
+ # Dynamically create a nested hash structure used to cache calls to +method_name+
+ # The cache method is named +#{method_name}_cache+ unless :as => :alternate_name
+ # is given.
+ #
+ # The hash structure is created using nested Hash.new. For example:
+ #
+ # def slow_method(a, b) a ** b end
+ #
+ # can be cached using hash_cache :slow_method, which will define the method
+ # slow_method_cache. We can then find the result of a ** b using:
+ #
+ # slow_method_cache[a][b]
+ #
+ # The hash structure returned by slow_method_cache would look like this:
+ #
+ # Hash.new do |as, a|
+ # as[a] = Hash.new do |bs, b|
+ # bs[b] = slow_method(a, b)
+ # end
+ # end
+ #
+ # The generated code is actually compressed onto a single line to maintain
+ # sensible backtrace signatures.
+ #
+ def hash_cache(method_name, options = {})
+ selector = options[:as] || "#{method_name}_cache"
+ method = self.instance_method(method_name)
+
+ args = []
+ code = "def #{selector}(); @#{selector} ||= "
+
+ (1..method.arity).each do |n|
+ args << "v#{n}"
+ code << "Hash.new {|h#{n}, v#{n}| h#{n}[v#{n}] = "
+ end
+
+ # Add the method call with arguments, followed by closing braces and end.
+ code << "#{method_name}(#{args * ', '}) #{'}' * method.arity} end"
+
+ # Extract the line number information from the caller. Exceptions arising
+ # in the generated code should point to the +hash_cache :...+ line.
+ if caller[0] && /^(.*):(\d+)$/ =~ caller[0]
+ file, line_number = $1, $2.to_i
+ else # We can't give good trackback info; fallback to this line:
+ file, line_number = __FILE__, __LINE__
+ end
+
+ # We use eval rather than building proc's because it allows us to avoid
+ # linking the Hash's to this method's binding. Experience has shown that
+ # doing so can cause obtuse memory leaks.
+ class_eval code, file, line_number
+ end
+ end
+
+ end
+end
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81 activesupport/test/caching_tools_test.rb
@@ -0,0 +1,81 @@
+require 'test/unit'
+require File.dirname(__FILE__)+'/../lib/active_support/caching_tools'
+
+class HashCachingTests < Test::Unit::TestCase
+
+ def cached(&proc)
+ return @cached if @cached
+
+ @cached_class = Class.new(&proc)
+ @cached_class.class_eval do
+ extend ActiveSupport::CachingTools::HashCaching
+ hash_cache :slow_method
+ end
+ @cached = @cached_class.new
+ end
+
+ def test_cache_access_should_call_method
+ cached do
+ def slow_method(a) raise "I should be here: #{a}"; end
+ end
+ assert_raises(RuntimeError) { cached.slow_method_cache[1] }
+ end
+
+ def test_cache_access_should_actually_cache
+ cached do
+ def slow_method(a)
+ (@x ||= [])
+ if @x.include?(a) then raise "Called twice for #{a}!"
+ else
+ @x << a
+ a + 1
+ end
+ end
+ end
+ assert_equal 11, cached.slow_method_cache[10]
+ assert_equal 12, cached.slow_method_cache[11]
+ assert_equal 11, cached.slow_method_cache[10]
+ assert_equal 12, cached.slow_method_cache[11]
+ end
+
+ def test_cache_should_be_clearable
+ cached do
+ def slow_method(a)
+ @x ||= 0
+ @x += 1
+ end
+ end
+ assert_equal 1, cached.slow_method_cache[:a]
+ assert_equal 2, cached.slow_method_cache[:b]
+ assert_equal 3, cached.slow_method_cache[:c]
+
+ assert_equal 1, cached.slow_method_cache[:a]
+ assert_equal 2, cached.slow_method_cache[:b]
+ assert_equal 3, cached.slow_method_cache[:c]
+
+ cached.slow_method_cache.clear
+
+ assert_equal 4, cached.slow_method_cache[:a]
+ assert_equal 5, cached.slow_method_cache[:b]
+ assert_equal 6, cached.slow_method_cache[:c]
+ end
+
+ def test_deep_caches_should_work_too
+ cached do
+ def slow_method(a, b, c)
+ a + b + c
+ end
+ end
+ assert_equal 3, cached.slow_method_cache[1][1][1]
+ assert_equal 7, cached.slow_method_cache[1][2][4]
+ assert_equal 7, cached.slow_method_cache[1][2][4]
+ assert_equal 7, cached.slow_method_cache[4][2][1]
+
+ assert_equal({
+ 1 => {1 => {1 => 3}, 2 => {4 => 7}},
+ 4 => {2 => {1 => 7}}},
+ cached.slow_method_cache
+ )
+ end
+
+end
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