From: Martin DeMello <martindemello@...>
Date: 2002-11-23T05:38:44+09:00
Subject: Re: [FAQ] Multiple constructors?

Nat Pryce <nat.pryce@b13media.com> wrote:
> On Fri, 2002-11-22 at 10:17, Martin DeMello wrote:
>> Nat Pryce <nat.pryce@b13media.com> wrote:
>> > If you want to have different constructors for different argument types,
>> > define different constructors on your class.  Your code will then be
>> > both more flexible and more readable.   E.g. If you had a class that
>> > could be created with either a String and a Regexp you would define
>> > constructors new_from_string(a_string) and new_from_regexp(a_regexp). 
>> 
>> This won't let me do something like 
>> 
>> my_objs = input_objs.map {|i| MyClass.new(i)}
> 
> That's true but how often does one put arbitrary objects into a
> collection and then use them to create something?  And if you do, you
> can easily put different types of objects into different collections.

Well, in general, I think that if you have to select on type at some
point in your code, it's neater to have it bundled into the constructor.
But now that you mention it, a better way to code the above might be
to have your class extend each object type it accepts with a method to
return the appropriately initialised instance, and avoid explicit type
dispatching altogether. Something like

  my_objs = input_objs.map {|i| i.newmyclass}

as you suggested I do with the generators.  

martin