# Method(std).call and send(sth) **URL:** \ **Category:** Rails\ **Created:** [August 3, 2007, 2:46pm UTC](https://www.ruby-forum.com/t/method-std-call-and-send-sth/111171 "2007-08-03T14:46:18Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![bartek](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/bcef8e/32.png) [@bartek](https://www.ruby-forum.com/u/bartek)\ **Post date:** [August 3, 2007, 2:46pm UTC](https://www.ruby-forum.com/t/method-std-call-and-send-sth/111171/1 "2007-08-03T14:46:18Z")
I’ve got two Models. A and B. Model A has an attribute “name”. Model B has an attribute “title”. I can get the name by a.method(:name).call I can NOT get the title by b.method(:title).call. Send works in both cases (a.send(:name), b.send(:title). I have rewritten my methods using send. But WHY did the former not work? ---
**Author:** ![bartek](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/bcef8e/32.png) [@bartek](https://www.ruby-forum.com/u/bartek)\ **Post date:** [August 4, 2007, 2:52am UTC](https://www.ruby-forum.com/t/method-std-call-and-send-sth/111171/2 "2007-08-04T02:52:29Z")
Bartek PuzoÅ„ wrote: > I’ve got two Models. A and B. Model A has an attribute “name”. Model B > has an attribute “title”. > > I can get the name by a.method(:name).call > I can NOT get the title by b.method(:title).call. > Send works in both cases (a.send(:name), b.send(:title). > > I have rewritten my methods using send. But WHY did the former not work? In model A you have something like: def name … end and in model B you don’t have the equivalent for title. Rails uses method\_missing to dynamically create column methods for you without you needing to explicitly create them in your model unless you want to override the default behavior or add new ones. send will follow the path through method\_missing, if it’s been defined, in search of the method to execute while method.call does not. I’m not a Ruby expert so I don’t know why there’s that difference. This is analogous to how respond\_to? will return true for methods that are defined through method\_missing but you don’t see them if you look at the methods array for that class. – Michael W. ---
**Author:** ![bartek](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/bcef8e/32.png) [@bartek](https://www.ruby-forum.com/u/bartek)\ **Post date:** [August 4, 2007, 3:01am UTC](https://www.ruby-forum.com/t/method-std-call-and-send-sth/111171/3 "2007-08-04T03:01:29Z")
Hi – On Fri, 3 Aug 2007, Michael W. wrote: > > I have rewritten my methods using send. But WHY did the former not work? > > without you needing to explicitly create them in your model unless you > > want to override the default behavior or add new ones. > > send will follow the path through method\_missing, if it’s been defined, > in search of the method to execute while method.call does not. I’m not a > Ruby expert so I don’t know why there’s that difference. > > This is analogous to how respond\_to? will return true for methods that > are defined through method\_missing but you don’t see them if you look at > the methods array for that class. Except… respond\_to? doesn’t do that 🙂 It really can’t, since method\_missing can do anything. You can sometimes (and people do) override respond\_to? so that it reflects what your method\_missing does, but it’s difficult if things are very dynamic. There was a thread about this on ruby-talk recently, with some interesting discussion of having a kind of third, high-level spec that could be used to define both method\_missing and respond\_to? to avoid having to do it all twice. I myself am not bothered by it; I think the implication of the “missing” in “method\_missing” is that the object does _not_ respond to the message, but a case can certainly be made that “respond” should include cases where the response is manufactured on the fly. David – - Books: RAILS ROUTING (new! [http://www.awprofessional.com/title/0321509242](http://www.awprofessional.com/title/0321509242)) RUBY FOR RAILS ([Ruby for Rails](http://www.manning.com/black)) - Ruby/Rails training & consulting: Ruby Power and Light, LLC ([http://www.rubypal.com](http://www.rubypal.com)) ---
**Author:** ![bartek](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/bcef8e/32.png) [@bartek](https://www.ruby-forum.com/u/bartek)\ **Post date:** [August 4, 2007, 4:20am UTC](https://www.ruby-forum.com/t/method-std-call-and-send-sth/111171/4 "2007-08-04T04:20:37Z")
On Fri, 3 Aug 2007, Michael W. wrote: > > > > I can get the name by a.method(:name).call > > > > > > and in model B you don’t have the equivalent for title. > > > > > > Rails uses method\_missing to dynamically create column methods for you > > > without you needing to explicitly create them in your model unless you > > > want to override the default behavior or add new ones. > > > > > > send will follow the path through method\_missing, if it’s been defined, > > > in search of the method to execute while method.call does not. I’m not a > > > Ruby expert so I don’t know why there’s that difference. Just to comment on this point: the reason is that if you do this: obj.method(“x”).call by the time you get to the .call part, you’ve already failed if there’s no “x” method. So call will never be called. > > > This is analogous to how respond\_to? will return true for methods that > > > are defined through method\_missing but you don’t see them if you look at > > > the methods array for that class. > > > > Except… respond\_to? doesn’t do that 🙂 It really can’t, since > > method\_missing can do anything. You can sometimes (and people do) > > override respond\_to? so that it reflects what your method\_missing > > does, but it’s difficult if things are very dynamic. > > So is Rails doing something funky with respond\_to? then to get that to work? Yes – respond\_to? is overriden in base.rb, and method\_missing is engineered in parallel, so that column names will be treated as methods and will also return true for respond\_to?. You can see a counter-example, where method\_missing and respond\_to? go in different directions, in the find\_by\_\* family of AR class methods: > > User.find\_by\_nick(“dblack”) > > =\> #\nil, … > > User.respond\_to?(“find\_by\_nick”) > > =\> false That’s basically what happens by default, while the behavior you’ve observed for the column names has to be brought about explicitly by overriding respond\_to? David – - Books: RAILS ROUTING (new! [http://www.awprofessional.com/title/0321509242](http://www.awprofessional.com/title/0321509242)) RUBY FOR RAILS ([Ruby for Rails](http://www.manning.com/black)) - Ruby/Rails training & consulting: Ruby Power and Light, LLC ([http://www.rubypal.com](http://www.rubypal.com)) ---
**Author:** ![bartek](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/bcef8e/32.png) [@bartek](https://www.ruby-forum.com/u/bartek)\ **Post date:** [August 4, 2007, 3:32am UTC](https://www.ruby-forum.com/t/method-std-call-and-send-sth/111171/5 "2007-08-04T03:32:31Z")
removed\_email\_address@domain.invalid wrote: > > > Send works in both cases (a.send(:name), b.send(:title). > > > > the methods array for that class. > > Except… respond\_to? doesn’t do that 🙂 It really can’t, since > method\_missing can do anything. You can sometimes (and people do) > override respond\_to? so that it reflects what your method\_missing > does, but it’s difficult if things are very dynamic. So is Rails doing something funky with respond\_to? then to get that to work? E.g. if I have: class Author \< ActiveRecord::Base def name end end class Post \< ActiveRecord::Base # title is column in Post end And then in script/console I get this: > > a = Author.new > > =\> #\nil}\> > > > a.method(“name”).call > > =\> nil > > > a.methods.grep(/name/) > > =\> [“name”, “table\_name\_prefix”, “attribute\_names”, “table\_name\_suffix”, > > “pluralize\_table\_names”] > > b = Post.new > > =\> #\nil}\> > > > b.method(“title”).call > > NameError: undefined method `title' for class`Post’ > > from (irb):5:in `method’ > > from (irb):5 > > > b.methods.grep(/title/) > > =\> [] > > > b.respond\_to?(“title”) > > =\> true > > > b.send(“title”) > > =\> nil – Michael W.