Why can't I assign "this" in a constructor?

[Thinkit]

It seems like a basic thing you'd want to do. It seems it only lets
you call an alternate constructor, this(...), as the first line in the
method. I want to be able to just say this=new MyObject(...) or
this=this.add(...).

I could just use a static method, but why don't I have the choice?

 

[Silvio Bierman]

It seems like a basic thing you'd want to do. It seems it only lets
you call an alternate constructor, this(...), as the first line in the
method. I want to be able to just say this=new MyObject(...) or
this=this.add(...).

I could just use a static method, but why don't I have the choice?

Why on earth would you want to assign a value to this. The 'this' reference
refers to the object a method is called upon which is not something that can
be changed in the method itself. C++ had an intermediate non-standard (and
very obscure) facility to assign to 'this' in a constructor to allow for
memory allocation overloading before explicit overloading of the 'new'
operator became available. Is that what you want to achieve?

If you want what is sometimes called a 'virtual constructor' you really need
some factory-like construct.

Silvio Bierman

 

[nos]

It seems like a basic thing you'd want to do. It seems it only lets
you call an alternate constructor, this(...), as the first line in the
method. I want to be able to just say this=new MyObject(...) or
this=this.add(...).

I could just use a static method, but why don't I have the choice?

Don't you at least have to do a cast? What if
this is a reference to an Integer, would this.add() even work?

 

[hiwa]

It seems like a basic thing you'd want to do. It seems it only lets
you call an alternate constructor, this(...), as the first line in the
method. I want to be able to just say this=new MyObject(...) or
this=this.add(...).

I could just use a static method, but why don't I have the choice?

'this' is a value, not a variable. In other words, it can't be an
lvalue of an expression.

 

[Tor Iver Wilhelmsen]

It seems like a basic thing you'd want to do. It seems it only lets
you call an alternate constructor, this(...), as the first line in the
method. I want to be able to just say this=new MyObject(...) or
this=this.add(...).

Because constructors are used from the outside: If the caller wants a
particular MyObject they can call the proper constructor.

An calling this() is't calling an _alternate_ constructor, but is
known as constructor chaining. The constructor you're in is still
_the_ constructor invoked.

I could just use a static method, but why don't I have the choice?

Because it's insane? You're trying to extend a constructor's role to
being a factory method, which is not what it's for: It's role is to
initiate *one* particular instance, referenced via the value this.

 

[Mark 'Kamikaze' Hughes]

It seems like a basic thing you'd want to do. It seems it only lets
you call an alternate constructor, this(...), as the first line in the
method. I want to be able to just say this=new MyObject(...) or
this=this.add(...).
I could just use a static method, but why don't I have the choice?

Because choice is bad, when there's already a right way to do it.
What are you trying to accomplish that isn't supported by this()?

 

[Thinkit]

Don't you at least have to do a cast? What if
this is a reference to an Integer, would this.add() even work?

If this has the method add(), this.add() will work. Apparently, this
can't be assigned as an l-value, though.