From: vasudevram <vasudevram@...>
Date: 2007-06-27T23:35:08+09:00
Subject: Re: Arguments into method calls?

On Jun 27, 7:26 pm, vasudevram <vasudev...@gmail.com> wrote:
> On Jun 27, 4:29 am, Tim Hunter <TimHun...@nc.rr.com> wrote:
>
>
>
>
>
> > Torrey Slattery wrote:
> > > I'm working on a program that takes user input via command line, then
> > > calls whatever method is related to that input text.
>
> > > For instance, if they type /help it calls the method help, if they type
> > > /quit it calls the method quit, /time calls time, etc.
>
> > > Essentially, if they type in something with a slash, I want the program
> > > to interpret it as a special command, strip off the / and calls a method
> > > with the leftover text.
>
> > > I can think of a clunky way to do this using a ton of if/elsif clauses
> > > and matching regular expressions, but as I eventually plan to have over
> > > a hundred commands, that doesn't seem pleasant to write at all.
>
> > > Is there a cleaner way to do this?
>
> > Check out the __send__ method, which lets you call a method whose name
> > is in a variable:
>
> > obj.__send__(method_name, args)
>
> > --
> > RMagick OS X Installer [http://rubyforge.org/projects/rmagick/]
> > RMagick Hints & Tips [http://rubyforge.org/forum/forum.php?forum_id=1618]
> > RMagick Installation FAQ [http://rmagick.rubyforge.org/install-faq.html]- Hide quoted text -
>
> > - Show quoted text -
>
> Tim Hunter is right. Just adding some details:
>
> You can create a hash that has the method names (as strings) as keys,
> and the same names (as symbols) as the corresponding values, e.g.:
>
> method_map = { "foo" => :foo, "bar" => :bar }
> # Insert code to read and parse your input command here - results in
> the command word (without the slash) being stored in the variable
> 'cmd', and the rest of the args in the variable 'args'; code is
> straightforward, so omitting for brevity.
> # Then:
>
> if method_map(cmd)
>     obj.send(method_map[cmd], args)
> else
>     raise StandardError, "Unrecognized command #{cmd}"
> end
>
> Note: The if condition might be wrong Ruby syntax - I've been
> switching between writing Python and Ruby pretty rapidly in the last
> few weeks while working on my projects - and don't remember right now
> what a reference to a hash element by key returns when the key doesn't
> exist in the hash (in Ruby, and am not at my machine right now) - I'm
> assuming it returns nil, in which case the code shown should work, but
> could be that I'm confusing it with the way it works in Python - where
> it returns None (Python equivalent to Ruby's nil) and in Ruby it may
> not return nil but throw an exception or whatever. Sorry about that.
> But shouldn't be a problem - just check the Ruby docs or even just, at
> an irb prompt, do:
>
> [].methods.sort
>
> This will show you the methods of the Hash class from which it should
> be easy to figure out what method can be used to test for the presence
> of a key in a hash. Modify the if statement accordingly.
>
> An even simpler way may be:
>
> obj.send(cmd.to_sym, args)
>
> In all the above code, I'm assuming that obj is an object of a class
> that implements all the methods needed to handle the commands
> supported.
>
> HTH
> Vasudev Ramhttp://www.dancingbison.comhttp://jugad.livejournal.comhttp://sourceforge.net/projects/xtopdf- Hide quoted text -
>
> - Show quoted text -

Forgot to add this (which I checked online before writing the previous
post):

  http://www.rubycentral.com/book/ref_c_object.html

Check out the __send__ and send method descriptions at that link.
__send__ is the same as send, its provided as an alternative in case
your class already has a send method of its own.

- Vasudev