From: "David A. Black" <dblack@...>
Date: 2009-09-22T11:23:31+09:00
Subject: Re: start_with

Hi --

On Tue, 22 Sep 2009, Rong wrote:

> Can someone explain why this doesn't work?
>
> class Person
>  attr_accessor :firstName
>
>  P=[]
>  def initialize
>    P << self
>  end
>  def self.find_person(part)
>    P.each {|e| if e.firstName.start_with(part) then return e end}

You mean start_with? (with question mark).

Also, you've got a bug. The #each method returns its receiver. That
means that if nothing triggers the return inside the block, you'll get
back the whole P array. See below....

>    end
>  end
>
>  u=Person.new
>  u.firstName="Ron"
>  r=Person.new
>  r.firstName="Bob"
>
>  q=Person.find_person("Ro")
>  puts q.firstName

p Person.find_person("nobody")

Output: [#<Person:0x1ee628 @firstName="Ron">, #<Person:0x1ee5d8
@firstName="Bob">]

What you want is:

   def self.find_person(part)
     P.find {|e| e.firstName.start_with(part) }
   end

which will return nil if nothing is found. (Also, first_name would be
more idiomatic than firstName, as a variable name.)

I've got reservations about using a constant as a modifiable array
like you're doing, but one (or two) thing(s) at a time :-)


David

-- 
David A. Black, Director
Ruby Power and Light, LLC (http://www.rubypal.com)
Ruby/Rails training, consulting, mentoring, code review
Book: The Well-Grounded Rubyist (http://www.manning.com/black2)