From: Robert Klemme <shortcutter@...>
Date: 2010-01-21T17:43:26+09:00
Subject: Re: about variable name and method name

2010/1/21 Ruby Newbee <rubynewbee@gmail.com>:
> class Array
>  def atoh
>     hash = Hash.new
>     if size % 2 != 0
>         raise "size must be odd"
>     end
>
>     0.step(size-1,2) do |c| hash[self[c]] = self[c+1] end
>     hash
>  end
> end

You are aware that there is Hash[] already, are you?

irb(main):004:0> a=%w{foo bar baz buz}
=> ["foo", "bar", "baz", "buz"]
irb(main):005:0> Hash[*a]
=> {"foo"=>"bar", "baz"=>"buz"}

Btw, you can shorten your method by using #each_slice.  I would do it like this:

irb(main):008:0> module Enumerable
irb(main):009:1> def to_hash
irb(main):010:2> h={}
irb(main):011:2> each_slice(2) {|k,v| raise "size must be odd" if v.nil?;h[k]=v}
irb(main):012:2> h
irb(main):013:2> end
irb(main):014:1> end
=> nil
irb(main):015:0> a.to_hash
=> {"foo"=>"bar", "baz"=>"buz"}
irb(main):016:0> a[0...-1].to_hash
RuntimeError: size must be odd
        from (irb):11:in `block in to_hash'
        from (irb):11:in `each_slice'
        from (irb):11:in `to_hash'
        from (irb):16
        from /opt/bin/irb19:12:in `<main>'
irb(main):017:0>

Disadvantage: it is not as safe as your solution because it will
detect an error even for Arrays with even number of elements if any
value is nil.

Advantage: it works for all Enumerables.

Synthesis:

module Enumerable
  def to_hash
    h = {}
    key = flag = nil

    each do |val|
      if flag
        h[key] = val
      else
        key = val
      end
      flag = !flag
    end

    raise 'odd!' if flag
    h
  end
end


> For "size" in the code above, we know it's a self.size method actually.
> But how ruby differ it's a variable or an instance method?

As soon as Ruby has seen an assignment it assumes a local variable.  Try this:

ruby -e 'def f;123;end;def g;p f;f=0;p f;end;g'

More details can be found here:
http://www.ruby-doc.org/docs/ProgrammingRuby/html/language.html#UO

Kind regards

robert


-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/