Array constructor references for multidimensional array

[bitter_fox]

Hi, Dan, Brian and Remi,
Thank you for your answers.

I agree that policy.

Regards,
bitter_fox


2013/5/8 Dan Smith <daniel.smith at oracle.com>

> On May 7, 2013, at 10:09 PM, bitter_fox <bitterfoxc at gmail.com> wrote:
>
> > Hi,
> > Array constructor references had been supported by [1].
> >
> > I have a question about multidimensional array constructor references.
> >
> > In my example, I use a two dimensional array of int, but other
> > multidimensional arrays have a same problem.
> >
> > We can write references for the one argument constructor of int[][]("new
> > int[x][]") by the change of [1]:
> >
> > interface F1
> > {
> >    int[][] f(int a);
> > }
> >
> > F1 f1 = int[][]::new;
> > f1.f(5); // means "new int[5][]"
> >
> >
> > We have another form of the array creation("new int[x][y]"), however the
> > compiler rejects references for it.
> >
> > interface F2
> > {
> >    int[][] f(int a, int b);
> > }
> >
> > F2 f2 = int[][]::new; // error
> > f2.f(5, 7);
> >
> > Is this the expected behavior?
>
> Yes.
>
> > I think it would be accepted because we can consider them as a two
> argument
> > constructor and it should treat them like a constructor of other type
> which
> > is not array.
> >
> > Is this already discussed?
>
> There's a trade-off.  This makes the expressions a little more powerful,
> but adds some complexity.  I'm not uncomfortable with the current behavior
> as a stable point, but I don't know how much others have thought about it
> and can raise the question with the Expert Group.
>
> Method references are essentially shorthand for lambda expressions.  We've
> selected a few common forms of lambda expressions to give them special
> treatment.  But there will always be something just slightly different that
> lives outside of the set we've chosen to support.  And in that case, the
> solution is to use a lambda expression instead:
>
> F2 f2 = (x,y) -> new int[x][y]; // vs. int[][]::new
>
> Another form that isn't supported by method references, but that someone
> might wish for, is one in which some method parameters are bound early:
>
> Function<Integer,String> f = i -> s.substring(0,i); // vs.
> s::substring(0,_) (for example)
>
> —Dan