Copy of object with attribute set in ruby

Question

Is it possible to return create copy of object with an attribute set, in Ruby?

Of course, a method can be defined to do this -

class URI::Generic
  def with_query(new_query)
    ret = self.dup
    ret.query = new_query
    ret
  end
end

But this might get a bit tedious to do with every attribute.

score 2 · Accepted Answer · edited May 23 '17 at 12:23

You can use options hash to pass multiple attribute-value pairs. Here is an illustrative example.

class Sample
  attr_accessor :foo, :bar

  def with(**options)
    dup.tap do |copy|
        options.each do |attr, value|
            m = copy.method("#{attr}=") rescue nil
            m.call(value) if m
        end
    end
  end

end


obj1 = Sample.new
#=> #<Sample:0x000000029186e0>
obj2 = obj1.with(foo: "Hello")
#=> #<Sample:0x00000002918550 @foo="Hello">
obj3 = obj2.with(foo: "Hello", bar: "World")
#=> #<Sample:0x00000002918348 @foo="Hello", @bar="World">

# Options hash is optional - can be used to just dup the object as well
obj4 = obj3.with
#=> #<Sample:0x0000000293bf00 @foo="Hello", @bar="World">

PS: There may be few variations on how to implement options hash, however, essence of approach will be more or less same.

Presumably some validation needs to be done on attr, to make sure it is a valid attribute name? — George Simms, Jan 02 '16 at 22:03
@GeorgeSimms Updated the answer to check for method existence. — Wand Maker, Jan 03 '16 at 08:13

Copy of object with attribute set in ruby

1 Answers1