Creating generic constructor in ruby

Question

I found this interesting answer :

https://stackoverflow.com/a/2348854/169277

This is ok when you're trying to set instance variables it works really great.

Is there a way to apply the same logic or better one to create generic constructor like :

def initialize(obj)
  obj.each do |k,v|
   #find the setter for each k and set the value v to and return newly created object
  end
end

If I had object TestObject:

class TestObject
attr_accessor :name, :surname, :sex
end

I was thinking to create it something like this:

TestObject.new({:name => 'Joe', :surname => 'Satriani'})

How would one achieve this?

So doing this would be a shorthand of :

t = TestObject.new
t.name = 'Joe'
t.surname = 'Satriani'

Gandalf StormCrow · Accepted Answer · 2013-07-17 21:37:20Z

1

Sure, you can use send to send arbitrary messages to an object. Since we're operating on self here, we can just invoke send directly.

def initialize(obj)
  obj.each do |k,v|
    send(:"#{k}=", v)
  end
end

For example, TestObject.new({:name => 'Joe'}) will call send "name=", "Joe".

edited Jul 17, 2013 at 21:37

Gandalf StormCrow

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answered Jul 17, 2013 at 21:30

Chris Heald

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4 Comments

Gandalf StormCrow Over a year ago

You were missing do after each (I edited), otherwise answer what I was looking for. thanks

Chris Heald Over a year ago

Sorry, I just copied the block out of the initial question. :)

Gandalf StormCrow Over a year ago

good point thanks, it's so much easier to judge other people haha

sawa Over a year ago

You don't need the colon.

Logan Serman · Accepted Answer · 2013-07-17 21:32:30Z

1

You can inherit from Struct to make a simple object, and then pass in the attributes to the initializer:

class TestObject < Struct.new(:name, :surname, :sex)
end

TestObject.new('Joe', 'Satriani') #=> sex will be nil

You can use OpenStruct to make quick value objects with arbitrary attributes:

t = OpenStruct(name: 'Joe', surname: 'Satriani')

You can include a module like Virtus: https://github.com/solnic/virtus

Or you can do what Chris Heald said.

answered Jul 17, 2013 at 21:32

Logan Serman

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Comments

Jörg W Mittag · Accepted Answer · 2013-07-17 22:28:56Z

0

I think it would be better to use keyword arguments for this. After all, the Hash keys are guaranteed to be valid Ruby identifier Symbols since they need to match up with method names. You don't need the capability to pass in arbitrary Ruby objects as keys of the Hash.

def initialize(**attrs)
  attrs.each do |attr, value| send(:"#{attr}=", value) end
end

TestObject.new(name: 'Joe', surname: 'Satriani')

answered Jul 17, 2013 at 22:28

Jörg W Mittag

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2 Comments

Arup Rakshit Over a year ago

I am familiar-ed with *attrs but what does it means **attrs ?

Jörg W Mittag Over a year ago

@Priti: It's the same but for keyword arguments. It collects all superfluous keyword arguments into a Hash, just like * collects all superfluous positional arguments into an Array.

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