Define a method that works on arrays of a specific type of object

In C# you can write an extension method like this:

public static Debt[] Foo(this Debt[] arr, int num)
{
    // Do something
}

This would allow you to use Foo() on an array of debts: debts.Foo(3)

Can you do this in Ruby? I know you can write a method that will work on arrays:

class Array
  def foo
    #开发者_Python百科 blah
  end
end

but this works on all types of arrays, not just an array of Debts

Thanks in advance.

the extend method is adding the instance methods to a particular object. so in you case it would be:

class YourClass
  def foo
    # blah
  end
end

debts.extend(YourClass)
debts.foo # now foo method is instance method of debts object

Actually it creates singleton class for debts object and then add to it the method. But you can't use this class, that's why it called "ghost" class

This would be a little tricky because Ruby arrays are not homogeneous. That is, you can store different types of objects inside of an array. That would lead me to a solution where I need to first verify that all objects in the array are of type Debt, and if they are then I can act on the array using foo.

You can continue to open up Array and add the foo method, but maybe you should create a FooArray instead and extend Array. This way you can redefine some methods such as << and push to ensure you only take Debts. Since you know that only Debts can be added to your array, you could call foo() without worry.

I believe you can do this by extending Ruby's Array class or better yet defining your own Array-like class and delegating the selected array methods to the native object.

Stack = Array.extract([
  :last,
  :push,
  :pop,
  :size,
  :clear,
  :inspect,
  :to_s
])

Why this is better than the alternative methods is explained here.