Multiple constructor in Ruby

ruby-talk
1

Hello!

I have a question about the constructor in Ruby.

Here is an exemple class :

class Test
  def initialize param
    puts param
  end
  def initialize param1, param2
    puts "#{param1} #{param2}"
  end
end

If I call the second constructor, everything works fine, whereas I got
an 'ArgumentError: wrong number of arguments (1 for 2)' with the first.

So, has the second constructor overriden the first one? Does that mean
you have to implement 'initialize' only once in a class?

Thank you!

···

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2

This is true for any method definition in Ruby, not just constructors.
There is no facility to select methods based on method signature, so
Ruby sees defining a method with the same name as an existing one as
replacing or overriding the original.

-Jeremy

···

On 11/18/2010 9:41 AM, Arturo Bonechi wrote:

Hello!

I have a question about the constructor in Ruby.

Here is an exemple class :

class Test
  def initialize param
    puts param
  end
  def initialize param1, param2
    puts "#{param1} #{param2}"
  end
end

If I call the second constructor, everything works fine, whereas I got
an 'ArgumentError: wrong number of arguments (1 for 2)' with the first.

So, has the second constructor overriden the first one? Does that mean
you have to implement 'initialize' only once in a class?

3

The answer to both of your questions is yes. Well, you *can* implement it
twice, but, as in your code, the first one is irrelevant. Remember that
while defining a class, all you're doing is executing code. Anyway, things
like default values and the hash options idiom make method overloading quite
unnecessary.

···

On Thu, Nov 18, 2010 at 10:41 AM, Arturo Bonechi <arturo.bonechi@gmail.com>wrote:

Hello!

I have a question about the constructor in Ruby.

Here is an exemple class :

class Test
def initialize param
   puts param
end
def initialize param1, param2
   puts "#{param1} #{param2}"
end
end

If I call the second constructor, everything works fine, whereas I got
an 'ArgumentError: wrong number of arguments (1 for 2)' with the first.

So, has the second constructor overriden the first one? Does that mean
you have to implement 'initialize' only once in a class?

Thank you!

--
Posted via http://www.ruby-forum.com/\.

4

Ok, thanks to both of you for those quick replies!

That explains a lot of things and solves my problem.

Thank you again!

···

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