Ruby accessing instance variable of other object

Question

I've been messing around with Ruby (Ruby 1.9.3, IRB 0.9.6(09/06/30)) and I'm trying to develop a complex number class. I have the initialize and to_s methods working fine. I'm now trying to overload the four arithmetic operators.

What I had is the following:

def +(other)
    return ComplexNumber.new(@real + other.@real, @imag + other.@imag)
end

but for some reason it didn't like other.@real; it says

syntax error: unexpected tIVAR

and points to the comma after other.@real.

So then I changed it to:

def get_values
    return [@real, @imag]
end

def +(other)
    other_values = other.get_values
    return ComplexNumber.new(@real + other_values[0], @imag + other_values[1])
end

Although this works, I have a feeling that it's not the correct way to do it. I don't really want to expose the get_values method; isn't there some way I can access a variable of another instance of the same class?

Ruby has a Complex class out of the box: puts '0.3-0.5i'.to_c.class #=>Complex — steenslag
– steenslag, Commented May 27, 2012 at 20:45

Sami A. Haija · Accepted Answer · 2012-05-27 19:46:00Z

3

The best way (in my opinion) would be to provide a read only access to the variables real and imag using attr_reader. Like:

class ComplexNumber
  attr_reader :imag, :real
  ...
  def +(other)
    return ComplexNumber.new(@real + other.real, @imag + other.imag)
  end
end

Note that attr_reader defines the methods on your behalf .real() and .imag() [attr_accessor additionally defines .real=() and .image=()]

answered May 27, 2012 at 19:46

Sami A. Haija

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4 Comments

wchargin Over a year ago

So the four methods are private, I assume?

Dave Newton Over a year ago

@WChargin Why do you assume that?

wchargin Over a year ago

Because there are set methods, which seem intrusive. Is it just the set methods that are private and the get methods are public?

Dave Newton Over a year ago

@WChargin No; they're all public. You can look up the docs for those methods (attr_accessor, attr_reader, etc.) too.

Dave Newton · Accepted Answer · 2012-05-27 19:39:38Z

1

Instance variables are accessed without the @ when referring to another instance:

other.real

(Assuming you're either using attr_accessor to define them, or are providing your own accessors. Even within the same instance you may prefer to use the accessors in case there's logic beyond simply returning the instance variable.)

answered May 27, 2012 at 19:39

Dave Newton

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2 Comments

wchargin Over a year ago

When I used other.real, it assumed real was a method and threw an error. What's attr_accessor?

Dave Newton Over a year ago

@WChargin apidock.com/ruby/Module/attr_accessor I don't know why you'd create a complex class without providing accessors for the different parts; almost anything with complex numbers would need them.

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