How can one set property values when initializing an object in Ruby?

Question

Given the following class:

class Test
  attr_accessor :name
end

When I create the object, I want to do the following:

t = Test.new {name = 'Some Test Object'}

At the moment, it results in the name attribute still being nil.

Is that possible without adding an initializer?

Answer 1

ok,

I came up with a solution. It uses the initialize method but on the other hand do exactly what you want.

class Test
  attr_accessor :name

  def initialize(init)
    init.each_pair do |key, val|
      instance_variable_set('@' + key.to_s, val)
    end
  end

  def display
    puts @name
  end

end

t = Test.new :name => 'hello'
t.display

happy ? :)

---

Alternative solution using inheritance. Note, with this solution, you don't need to explicitly declare the attr_accessor!

class CSharpStyle
  def initialize(init)
    init.each_pair do |key, val|
      instance_variable_set('@' + key.to_s, val)
      instance_eval "class << self; attr_accessor :#{key.to_s}; end"
    end
  end
end

class Test < CSharpStyle
  def initialize(arg1, arg2, *init)
    super(init.last)
  end
end

t = Test.new 'a val 1', 'a val 2', {:left => 'gauche', :right => 'droite'}
puts "#{t.left} <=> #{t.right}"

Answer 2

As mentioned by others, the easiest way to do this would be to define an initialize method. If you don't want to do that, you could make your class inherit from Struct.

class Test < Struct.new(:name)
end

So now:

>> t = Test.new("Some Test Object")
=> #<struct Test name="Some Test Object">
>> t.name
=> "Some Test Object"