From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2010-09-29T16:06:22+09:00
Subject: Re: Error - "`+': can't convert nil into String"

On Wed, Sep 29, 2010 at 5:03 AM, Paul Roche <prpaulroche@gmail.com> wrote:
>
> Why does the code below give me this error? What can I do to fix it?
>
> /people3.rb:4:in `+': can't convert nil into String (TypeError)
> om C:/Ruby192/people3.rb:4:in `to_s'
>
> class Person
> attr_accessor :fname, :lname, :age
> def to_s
> "hi " + @fname + ", " + @lname
> end
>
> end

@fname is nil, and you are trying to call the + method on it. Hence the error.
The recommended way would be something like:

class Person
  attr_accessor :fname, :lname, :age
  def to_s
    "hi #{@fname}, #{@lname}"
  end
end

irb(main):001:0> class Person
irb(main):002:1>   attr_accessor :fname, :lname, :age
irb(main):003:1>   def to_s
irb(main):004:2>     "hi #{@fname}, #{@lname}"
irb(main):005:2>   end
irb(main):006:1>
irb(main):007:1* end
=> nil
irb(main):008:0> Person.new.to_s
=> "hi , "
irb(main):009:0> p = Person.new
=> hi ,
irb(main):010:0> p.lname = "Smith"
=> "Smith"
irb(main):011:0> p.to_s
=> "hi , Smith"
irb(main):012:0> p.fname = "John"
=> "John"
irb(main):013:0> p.to_s
=> "hi John, Smith"

Jesus.