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From: "G.B." <bauhaus@futureapps.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Quick question regarding limited type return syntax
Date: Mon, 04 Aug 2014 12:42:42 +0200
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Xref: news.eternal-september.org comp.lang.ada:21434
Date: 2014-08-04T12:42:42+02:00
List-Id: <comp.lang.ada>

On 04.08.14 11:24, Niklas Holsti wrote:
> As I understand it, even in the languages which do
> have specific constructor/destructor facilities, there is no requirement
> or check that a constructor must initialize all the components of the
> object (but I'm not sure how Java works in this case).


Java lets you write Ada:

class T
{
     public T() {
         this.foo();
     }
     protected void foo() {}
}

class S extends T
{
     public Integer I;
     public S() {
         // calls super
         // I not initialized (and not allocated)
         this.I = 1;
     }

     @Override
     protected void foo() {
         this.I += 1;
     }
}

class Dispatching
{
     public static void main(String[] args) {
         S Y = new S();
     }
}

This program will stop after throwing a NullPointerException.
If S.I is made an int, the default value is 0, and the above
program is considered bad style(*).
   C++, I think, lets "this" stand for the type at the current "level"
during construction, so there is no dispatching to lower levels IIUC;
however, Stroustrup mentions some pointer tricks that let the
programmer circumvent the restriction.


(*) http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html