From: Dave Thomas <dave@...>
Date: 2003-08-13T02:49:52+09:00
Subject: Re: common constructor idioms

Scott Thompson wrote:

> In C++ one often declares a constructor that accepts another instance of 
> this class.  For those familiar with C++ syntax I'm talking about:
> 
> class MyClass {
>     /* other interesting stuff in this class deleted */
> 
>     /* Copy constructor */
>     MyClass(const MyClass &objectToCopy);
> };
> 
> I guess you could do something similar in Ruby like this:
> 
> class MyClass
>     def initialize(x)
>         if x.class == MyClass then
>             #some code to duplicate stuff in x
>         else
>             #potentially other initialization mechanisms here
>         end
>     end
> end
> 
> 
> Though there are bound to be differing opinions on the subject (and I 
> have no desire to start a flame war so please be kind) I was curious to 
> know is a popular idiom in Ruby code or not?  More to the point, would 
> someone who was using an Ruby extension reasonably assume that this 
> initialization mechanism was included?

Personally I wouldn't overload #new like this. Instead I'd add a new 
static construction method

     class Boat
        def Boat.from_other_boat(b)
           # ...
        end
     end


...or... I'd simply implement an instance method to duplicate a 
particular object.

I wrote a blog entry on constructors:

http://pragprog.com/pragdave/Practices/ConstructionMethods.rdoc,v


Cheers


Dave