[ruby-talk:18577] Re: ruby versus Perl Magic

On Fri, 27 Jul 2001 01:12:33 +0900, markus jais <[e-mail]> wrote:

> --------------------
> 	#!/usr/local/bin/ruby -w
> 
> 	i = 1
> 	a = i + ARGV[0]
> 	print a, "\n"
> ------------------
> the error I get:
> ./my.rb:4:in `+': String can't be coerced into Fixnum (TypeError)
>         from ./my.rb:4
> 
> Obviously the Perl Magic does not work in Ruby.
> I have to write  ARGV[0].to_i
> 
> Does Ruby also support "Magic" as some Perl folks call this
> that is, to convert variables automatically when used in a
mathematical
> expression.
> if yes, how can I tell Ruby to be magic

You can override the + operator on Strings and Fixnum (see below). But
what result do you expect in the expression "1" + "4" (both Strings)?

irb(main):020:0> 1 + "4"
5
irb(main):021:0> "2" + 3
5
irb(main):022:0> "1" + "4"
"14"

The last one might explain why Ruby isn't "magic". How do you
differenciate concatenation and addition?
You could 'add' strings if they are only digits, but how can you concat
them then?
You might need another operator (or method) to concat strings. Then you
could have '+' to only add elements in the numeric way. But that's
incompatible with other ruby scripts.

---------
class Fixnum # should be more generic, but Numeric doesn't respond to :+
  alias :_old_plus :+

  def +(other)
    _old_plus other.to_i
  end
end

class String
  alias :_old_plus :+

  def +(other)
    if other.is_a? Fixnum # Numeric?
      to_i + other
    else
      _old_plus other
    end
  end
end
----------

Mike.
midulo.