From: "Hal E. Fulton" <hal9000@...>
Date: 2003-07-16T01:20:49+09:00
Subject: Re: How to reduce Ruby runtime error?

----- Original Message ----- 
From: "Xiangrong Fang" <xrfang@hotmail.com>
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Tuesday, July 15, 2003 11:05 AM
Subject: How to reduce Ruby runtime error?


> Hi my friends,
> 
> I am thinking of how can I reduce Ruby runtime error. Not like
> languages such as C or Pascal, Ruby is typeless. This is a good thing,
> especially in design time. However, I found that my application is not
> stable due to this feature.
> 
> For example, a routine is expecting a string, and this string turned out
> to be nil at runtime, an error occurred. In Delphi, for example, it is
> impossible that a string becomes a nil, it will be an empty string.
> 
> How can I better utilize Ruby's typeless feature yet avoid such anonying
> runtime problem?

You can always check types explicitly if you
really want to:

    raise "Expecting an array" if not x.is_a? Array

Or you could test for nil:

    raise "Argument was nil" if x.nil?

You can test for methods available ("duck typing")
rather than actual class:

    raise "Object has no 'push' method" if not x.respond_to? :push

You can check for the "magic" conversion methods such as
to_str and to_ary:

    if not x.is_a? String
      x = x.to_str if x.respond_to? :to_str
    else
      raise "Wanted a string"
    end

Not recommended: You could convert a nil value on entry
into the method:

    x = [] if x.nil?

Not recommended: You could modify the NilClass so that a
nil value acted the way you want:

    class NilClass
      def +(value)
        value       # nil + x always equals x
      end
    end

I'm sure there are other ways.

Hal

--
Hal Fulton
hal9000@hypermetrics.com