Re: Constructors?

Francis Barber wrote:
> Byron Foster wrote:
>> I was wonder why it is necessary to call a constructor from within
>> an exsisting constructor. I found the following to be confusing
>> when trying to define a default constructor.
>> 
>> public class Test { }
>> 
>> new Test() { println ("Constructing Test, 123"); this(); }
>> 
>> The above will not compile with the following error:
>> 
>> nice.lang: parsing foo: parsing foo: typechecking
>> 
>> ~/nice/./foo/Test.nice: line 8, column 3: Ambiguity for symbol
>> this. Possibilities are : foo.Test <init>() foo.Test <init>()
>> 
>> I assume this is occuring because there is an automatic constructor
>> and the Test() constructor that I have now defined. However, this
>> seems to be a likely case.
>> 
>> Also,  Is it possible to declare a constructor within the class
>> definition?
 >
 > I'm not the expert on this topic, but the way I see it the
 > constructor you have defined is actually calling itself recursively.
 > As there is no base case, the recursion will continue indefinitely
 > and so object of type Test can ever be instantiated.  I imagine this
 > is illegal in most, if not all, object oriented languages.  The
 > problem here is probably that the Nice error message is misleading,
 > to say the least.  This is what Java has to say about it.
 >
 > public class Test { public Test() { this();
 > System.out.println("Hello"); } }
 >
 > javac Test.java
 >
 > Test.java:3: Recursive constructor invocation: Test(). this();
 >
 > I'm not sure about the last question: "Also,  Is it possible to
 > declare a constructor within the class definition?"  What I would
 > say, though, is that Nice's default constructor is pretty powerful
 > and it is often unnecessary to define your own.  Don't forget that
 > you can use an initialisation block if you need to.  See
 > http://nice.sourceforge.net/manual.html#constructor and
 > http://nice.sourceforge.net/manual.html#id2429177

Arjan provided the following response to this same question I posted on 
the sourceforge forums:

http://sourceforge.net/forum/forum.php?thread_id=1155614&forum_id=40268

There seems to be some discussion surrounding this issue.  After reading 
the discussions I think I understand the design decisions better. 
Certainly given the fact that one cannot access member variables from 
within a constructor I guess it wouldn't make much since not to call the 
automatic constructor, or some chain of constructors that end with an 
automatic constructor.  Otherwise, nothing in the instance changes.  I 
wonder if the Nice constructor approach aids in better compilation and 
object creation performance, or if it is strictly language motivated?



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