From: Florian Frank <flori@...>
Date: 2007-10-11T18:34:21+09:00
Subject: Re: Why does this use a block

Anonymous wrote:
> So I'm new to Ruby and I'm trying to use OptionParser to parse in some
> command line arguments. I looked at some documentation on OptionParser and
> there is something that's confusing me to no end. In all the examples a
> block is being passed in to the constructor of the OptionParser object. The
> constructor simply makes a yield call, passing self as an argument. 
>
> What is the point of this? Can we not convert
>
> opts = OptionParser.new() {|opts| body}
>
> To
>
> opts = OptionParser.new()
> body
>
> ? This seems more natural to me. But the former seems like a common Ruby
> idiom so I'm wondering what I am missing.
>   
You might want to use the shortcut

option_parser = OptionParser.new do |o|
  o.foo = "foo"
  o.bar = "bar"
  ...
end

during initialization of the object instead of using the long name, that
will be used later in the program after you forgot, what "o" meant.

I don't know if this is the case with OptionParser, but many methods
also want to do some housekeeping after the execution of the block, for
example, open(...) do |f| ... end closes the opened file. A constructor
might want to check his configuration (given in the block) and raise an
exception, if errors were found. This is better than creating a wrongly
configured object, that only will throw an exception later in the program.

-- 
Florian Frank