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James Byrne

2009-Apr-17 18:47 UTC

When is nil not false?

Can someone see what I cannot given this code?

class ForexCASource

  def initialize(source=nil)
    xchg_source unless source
    puts "this is source = #{source} #{source.class}"
    puts "do we get here? why?"
    xchg_source(source)
  end

>> fx = ForexCASource.newthis is source =  NilClass
do we get here? why?
TypeError: can''t convert nil into String
        from /usr/lib/ruby/1.8/open-uri.rb:32:in
`open_uri_original_open''
        from /usr/lib/ruby/1.8/open-uri.rb:32:in `open''
        from
/home/byrnejb/Software/Development/Projects/proforma.git/app/services/forex_ca_source.rb:58:in
`xchg_source''
        from
/home/byrnejb/Software/Development/Projects/proforma.git/app/services/forex_ca_source.rb:52:in
`initialize''
        from (irb):1:in `new''
        from (irb):1>> -- 
Posted via http://www.ruby-forum.com/.

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Gary Doades

2009-Apr-17 18:53 UTC

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Re: When is nil not false?

James Byrne wrote:> Can someone see what I cannot given this code?
> 
> class ForexCASource
> 
>   def initialize(source=nil)
>     xchg_source unless source
>     puts "this is source = #{source} #{source.class}"
>     puts "do we get here? why?"
>     xchg_source(source)
>   end
> 
> 
>>> fx = ForexCASource.new
> this is source =  NilClass
> do we get here? why?
> TypeError: can''t convert nil into String
>         from /usr/lib/ruby/1.8/open-uri.rb:32:in
> `open_uri_original_open''
>         from /usr/lib/ruby/1.8/open-uri.rb:32:in `open''
>         from
>
/home/byrnejb/Software/Development/Projects/proforma.git/app/services/forex_ca_source.rb:58:in
> `xchg_source''
>         from
>
/home/byrnejb/Software/Development/Projects/proforma.git/app/services/forex_ca_source.rb:52:in
> `initialize''
>         from (irb):1:in `new''
>         from (irb):1
xchg_source unless source

This is a one-liner that just doesn''t call xchg_source if source is nil
(which it is in this case).

All other lines will execute normally so:

xchg_source(source) will call xchg_source with a nil value. Since you 
haven''t posted the code for xchg_source it''s hard to tell
what''s
happening in there.

did you mean:

      if !source
        puts "this is source = #{source} #{source.class}"
        puts "do we get here? why?"
        xchg_source(source)
      end

Cheers,
Gary,


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James Byrne

2009-Apr-17 18:55 UTC

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Re: When is nil not false?

James Byrne wrote:> Can someone see what I cannot given this code?
I need a return in front of the statement.

  def initialize(source=nil)
    return xchg_source unless source
    xchg_source(source)
  end
-- 
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Robert Walker

2009-Apr-18 01:28 UTC

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Re: When is nil not false?

James Byrne wrote:> James Byrne wrote:
>> Can someone see what I cannot given this code?
> 
> I need a return in front of the statement.
> 
>   def initialize(source=nil)
>     return xchg_source unless source
>     xchg_source(source)
>   end
Why not just let xchg_source deal with the nil then you just have:

def initialize(source=nil)
  xchg_source(source)
end

protected # assuming this is not part of the public interface
def xchg_source(source)
  if source
    # whatever you do if source is given
  else
    # whatever should happen if source is nil
  end
end
-- 
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James Byrne

2009-Apr-18 01:32 UTC

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Re: When is nil not false?

Robert Walker wrote:
> Why not just let xchg_source deal with the nil then you just have:
> 
> def initialize(source=nil)
>   xchg_source(source)
> end
> 
> protected # assuming this is not part of the public interface
Ah, but it is public and if I pass a nil object to it then it fails, but 
it does not fail if I pass it nothing at all, or if I pass it a string, 
or a file object, etc.  Odd, but there it is.

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Andrius Chamentauskas

2009-Apr-18 13:25 UTC

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Re: When is nil not false?

What about:
def initialize(source=nil)
  source ? xchg_source(source) : xchg_source
end

Or if you prefer longer notation
def initialize(source=nil)
  if source
    xchg_source(source)
  else
    xchg_source
end

Or like in your example:
def initialize(source=nil)
  return xchg_source unless source
  xchg_source(source)
end

On Apr 17, 9:47 pm, James Byrne
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:> Can someone see what I cannot given this code?
>
> class ForexCASource
>
>   def initialize(source=nil)
>     xchg_source unless source
>     puts "this is source = #{source} #{source.class}"
>     puts "do we get here? why?"
>     xchg_source(source)
>   end
>
> >> fx = ForexCASource.new
>
> this is source =  NilClass
> do we get here? why?
> TypeError: can''t convert nil into String
>         from /usr/lib/ruby/1.8/open-uri.rb:32:in
> `open_uri_original_open''
>         from /usr/lib/ruby/1.8/open-uri.rb:32:in `open''
>         from
>
/home/byrnejb/Software/Development/Projects/proforma.git/app/services/forex_ca_source.rb:58:in
> `xchg_source''
>         from
>
/home/byrnejb/Software/Development/Projects/proforma.git/app/services/forex_ca_source.rb:52:in
> `initialize''
>         from (irb):1:in `new''
>         from (irb):1
>
> --
> Posted viahttp://www.ruby-forum.com/.--~--~---------~--~----~------------~-------~--~----~
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