From: Stefano Crocco <stefano.crocco@...>
Date: 2008-08-29T05:12:31+09:00
Subject: Re: Use a string as a method call

On Thursday 28 August 2008, Chris Bailey wrote:
>  I'm trying to come up with an efficient way of using user input as a
> way of calling methods. I'm unhappy with the way that I am doing it
> because it isn't very flexible. This is what I'm doing now.
>
> input = gets.downcase.chomp
>
> if input == foo
>     do_foo()
> elsif input == bar
>     do_bar()
> else
>     puts "That isn't a command!"
> end
>
> What I would like to do is more like so.
>
> commands = {
>             'foo'   =>      do_foo(),
>             'bar'   =>      do_bar()
>            }
>
> I then would like to search the commands hash for a key that matches the
> player input and execute the method associated with that key. What I've
> noticed is that upon initialization of the hash the value becomes equal
> to the result of the method but that is not what I want. If I store the
> value as a string ie "do_foo()" would I be able to parse that string and
> execute it as a method? And if so, how would that be done?

You can do something like this:

method_name = gets.downcase.chomp
send method_name

send is a method which takes as a first argument a method name (as a string or 
symbol) and calls that method on its receiver, passing all the remaining 
arguments to it (see ri Object#send for a better explaination). To better 
handle the possibility the user inserts a wrong string, you can rescue the 
NoMethodError exception:

method_name = gets.downcase.chomp
begin
  send method_name
rescue NoMethodError
  puts "#{method_name} is not a valid command"
end

If you want to restrict the methods the user can call, store them in an array 
and check whether the string he entered is there before calling send:

commands = %w[foo bar]
method_name = gets.downcase.chomp
if commands.include? method_name then send method_name
else puts "#{method_name} is not a valid command"
end

I hope this helps

Stefano