From: ptkwt@... (Phil Tomson)
Date: 2004-08-19T04:51:15+09:00
Subject: Re: When to use parentheses around method args?

In article <cfvmk2$cao$1$8300dec7@news.demon.co.uk>,
Richard Dale  <Richard_Dale@tipitina.demon.co.uk> wrote:
>On Patrick Logan's blog he gives a ruby example in discussing design

>trade-offs implementing a visitor/decorator pattern with search trees that
>are a mixture of elephants and boxes of elephants. 
>
>http://martinfowler.com/bliki/CourtesyImplementation.html
>
>But I just couldn't work out what the code meant at first - it took me about
>5 mins of staring at it before the penny dropped..
>
<snip>
>My problem was the the method:
>
>  def << aNode
>    @children << aNode
>  end
>
>I wondered what is this strange new ruby syntax? But as soon as I saw it
>meant this I could follow the code:
>
>  def <<(aNode)
>    @children << aNode
>  end
>
>It's like one of the 'Escher mind teasers' where you seen a cube from one
>perspective, and then suddenly your brain flip-flops to another one.
>
>Are there any rules of thumb for when it's a good idea to leave out the
>brackets and when to use them?

When I'm defining an operator method (like '<<' in this example) I always 
put in the parens - it's just clearer.  Actually, in general when I'm 
defining any method I always use the parens.  When I call a method, 
though, I often omit the parens.

>
>He says it's bad style to use 'if c.kind_of? Elephant', and instead it's
>better to expect each node to return a number of elephants. His improved
>example expects every node to respond to 'num_elephants', but he makes no
>check and so there would be a method_missing execption thrown for a
>non-elephant/non-box thing.
>
>I think the second example would be improved by a respond_to? check, but
>what if you expected 'elephant aware nodes' to return you a total elephant
>weight? Has anyone suggested adding a 'conforms_to?' check in ruby that
>checks that an instance will respond_to? an Array of method name symbols?
>

I must admit I wasn't satisfied with the solution presented there either.  
I suppose if you've got a limited number of leaf-type Nodes it's not so 
bad, but if you've got lots of leaf types then you have to include more 
methods to handle them.  

Phil