From: Luc Heinrich <lucsky@...>
Date: 2002-04-05T02:48:01+09:00
Subject: Re: Test the result of an initialization ?

On 4/04/2002 18:52, "Jayce Piel" <jayce@mosx.net> wrote:

> By putting begin/rescue code around all call to #new, the code begins to
> be unreadable...

Uh, that's highly debatable, but I won't bite (at least not here)... ;-)

Anyway, if you *really* want to use the 'return-nil-on-error' creation
pattern, why don't you use a factory method in your class ? Like...

class ArchiveFile

  private_class_method :new

  def ArchiveFile.create( name )
     return new(name) if (name.is_valid_and_stuff?)
     return nil 
  end
  ...
end

...and then do...

foo = ArchiveFile.create( "/hoink/gruik/woof/archive.tar" )
if foo.nil?
  puts "Crap!"
else
  foo.do_something_useful
  foo.close
end

...which *really* looks ugly, if you ask me. A much better way to do that
would be to take the Ruby way (of course) and use the open-with-block style,
like that:

class ArchiveFile

  private_class_method :new

  def ArchiveFile.open( name )
    if (name.is_valid_and_stuff?)
      archive_file = new( name )
      yield( archive_file )
      archive_file.close
    end
  end
  ...
end

...and then do...

ArchiveFile.open( "/hoink/gruik/woof/archive.tar" ) do |archive_file|
  archive_file.do_something_useful
end

... which:
1. Ensure that the block is executed *only* if the parameter is valid.
2. Automatically close the archive file when the block ends.
3. Looks much nicer... :-)

Depending on what you want, this might be a better solution.

And on a more general note, you really shouldn't try to apply patterns or
idioms from other languages when Ruby have a specific (and usually better
:-) ) approach.

-- 
Luc - lucsky@mac.com