From: dblack@...
Date: 2006-04-15T00:50:32+09:00
Subject: Re: Default value for any type?

Hi --

On Fri, 14 Apr 2006, Victor Shepelev wrote:

>>> Hello all.
>>>
>>> I have code:
>>>
>>> def create_default(type)
>>>   type.new
>>> end
>>>
>>> But with, for example, Float, it suddenly said:
>>>
>>> create_default(Float) #<=== undefined method `new' for Float:Class
>>> (NoMethodError)
>>>
>>> Hmmm? How can I uniformly obtain default value for given class?
>>
>> What should the default value for a Float be? What are you trying to
>> really do here?
>>
>> There are a number of classes that you're not going to be able to call
>> #new on.
>
> Not so long time ago I've been a C++ guy. There we could do:
> float(); //0.0
> int(); //0
> ...etc...
>
> Generalized version:
> template<typename T>
> T create_default()
> {
>  return T();
> }
>
> //usage:
> create_default<float>();       // => 0.0
> create_default<std::string>(); // => ""
>
> and so on. I think, argument-less constructor, creating some "default"
> value, is a very useful thing.
>
> (yes, I can define Float#default and so on for myself ;) But I want to know,
> *why*?)

I guess that's what I want to know too: why would you expect Ruby
classes to have default instances, and why would you need them too?


David

-- 
David A. Black (dblack@wobblini.net)
Ruby Power and Light, LLC (http://www.rubypowerandlight.com)

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