Rubyでクラスがどこで定義されているか調べる

Method#source_location はあるが、Class#source_location はない。そもそもクラス定義が複数のファイルにわたっていることも多いので、あったとしてもたいして意味はない。

それでは、あるクラスの（インスタンス）メソッドがどこで定義されているか調べたらどうか？

Rails.class.instance_methods(false).map { |s| Rails.method(s).source_location }.compact.map { |x| x[0] }.sort.uniq.map { |x| x.sub(/\A.*2.0.0./, '') }

=> ["pp.rb",
 "psych/core_ext.rb",
 "gems/activesupport-3.2.11/lib/active_support/core_ext/module/aliasing.rb",
 "gems/activesupport-3.2.11/lib/active_support/core_ext/module/anonymous.rb",
 "gems/activesupport-3.2.11/lib/active_support/core_ext/module/attr_internal.rb",
 "gems/activesupport-3.2.11/lib/active_support/core_ext/module/attribute_accessors.rb",
 "gems/activesupport-3.2.11/lib/active_support/core_ext/module/delegation.rb",
 "gems/activesupport-3.2.11/lib/active_support/core_ext/module/deprecation.rb",
 "gems/activesupport-3.2.11/lib/active_support/core_ext/module/introspection.rb",
 "gems/activesupport-3.2.11/lib/active_support/core_ext/module/method_names.rb",
 "gems/activesupport-3.2.11/lib/active_support/core_ext/module/qualified_const.rb",
 "gems/activesupport-3.2.11/lib/active_support/core_ext/module/reachable.rb",
 "gems/activesupport-3.2.11/lib/active_support/core_ext/module/remove_method.rb",
 "gems/activesupport-3.2.11/lib/active_support/core_ext/module/synchronization.rb",
 "gems/activesupport-3.2.11/lib/active_support/core_ext/object/duplicable.rb",
 "gems/activesupport-3.2.11/lib/active_support/dependencies.rb",
 "gems/activesupport-3.2.11/lib/active_support/deprecation/method_wrappers.rb",
 "gems/debugger-1.6.0/lib/ruby-debug-base.rb",
 "gems/liquid-2.5.0/lib/liquid/module_ex.rb",
 "gems/rake-0.9.2.2/lib/rake/ext/core.rb",
# (snip)

なんだかワサワサ出てきた。

参考文献: Rubyのメソッドを数えましょう♫