Rails code segment explained

Question

I am working on an app which has the below code:

def app
  @app ||= begin
    if !::File.exist? options[:config]
      abort "configuration #{options[:config]} not found"
    end

    app, myoptions = Rack::Builder.parse_file(self.options[:config], opt_parser)
    self.myoptions.merge! myoptions
    app
  end
end

I am struggling to get my head around several parts of it..

@app||= begin...end

Does this mean that if @app does not exist the block is run?

app ,options = rack::builder

What does the comma do to it?

Please help

Craig Taub · Accepted Answer · 2013-02-08 09:54:12Z

2

Your first assumptions was correct, it does say that if @app is nil, set it to whatever is returned in the block delimited with begin, end.

Regarding the comma, it works like this:

avar, bvar = "atest", "btest"

If you look at the source for Rack:Builder.parse_file then you will notice the last line

return app, options

So it is returning two values.

Hope that helps

answered Feb 8, 2013 at 9:54

Craig Taub

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Comments

Jahan Zinedine · Accepted Answer · 2013-02-08 10:11:59Z

1

@Craig-Taub ansewered the question,
I just want to add some notes:

Ruby commands are expressions which means they return value and you can assign them to variables.
You can read more about expressions and statements on Wikipedia and PragProg.

Second is that when you return more than one value in a code block, Ruby will wrap it into a simple array and return it to the caller.
That's why it works like that.

edited Feb 8, 2013 at 10:11

answered Feb 8, 2013 at 10:06

Jahan Zinedine

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