@@ -1680,7 +1680,47 @@ The method +Range#overlaps?+ says whether any two given ranges have non-void int h3. Extensions to +Proc+ -... +h4. +bind+ + +As you surely know Ruby has an +UnboundMethod+ class whose instances are methods that belong to the limbo of methods without a self. The method +Module#instance_method+ returns an unbound method for example: + +<ruby> +Hash.instance_method(:delete) # => #<UnboundMethod: Hash#delete> +</ruby> + +An unbound method is not callable as is, you need to bind it first to an object with +bind+: + +<ruby> +clear = Hash.instance_method(:clear) +clear.bind({:a => 1}).call # => {} +</ruby> + +Active Support defines +Proc#bind+ with an analogous purpose: + +<ruby> +Proc.new { size }.bind([]).call # => 0 +</ruby> + +As you see that's callable and bound to the argument, the return value is indeed a +Method+. + +NOTE: To do so +Proc#bind+ actually creates a method under the hood. If you ever see a method with a weird name like +__bind_1256598120_237302+ in a stack trace you know now where it comes from. + +Action Pack uses this trick in +rescue_from+ for example, which accepts the name of a method and also a proc as callbacks for a given rescued exception. It has to call them in either case, so a bound method is returned by +handler_for_rescue+, thus simplifying the code in the caller: + +<ruby> +def handler_for_rescue(exception) + _, rescuer = Array(rescue_handlers).reverse.detect do |klass_name, handler| + ... + end + + case rescuer + when Symbol + method(rescuer) + when Proc + rescuer.bind(self) + end +end +</ruby> h3. Extensions to +Date+ railties/guides/source/active_support_core_extensions.textile d226287855800e1eec58cd35ed3aac5cd9fbf630 Xavier Noria fxn@hashref.com http://github.com/lifo/docrails/commit/f37c90a8758d4dc007ad6a3428769651981ea4f4 f37c90a8758d4dc007ad6a3428769651981ea4f4 2009-10-26T16:11:22-07:00 2009-10-26T16:11:22-07:00 AS guide: documents Proc#bind 41b0af00875a76c6002c3afc24e359d753c734b9 Xavier Noria fxn@hashref.com