A peek at the roadmap for pattern matching and more

[Remi Forax]

> De: "Brian Goetz" <brian.goetz at oracle.com>
> À: "amber-spec-experts" <amber-spec-experts at openjdk.java.net>
> Envoyé: Mercredi 12 Août 2020 22:44:04
> Objet: A peek at the roadmap for pattern matching and more

> Several folks have asked that I sketch out a little more of the roadmap for
> pattern matching, so that we can better evaluate the features being discussed
> now (since, for example, the semantics of pattern matching are heavily
> influenced by nested patterns.)

> I've checked into two drafts which are VERY ROUGH, but which correspond to the
> next two logical increments after patterns in switch.

> Deconstruction patterns:

> [
> https://github.com/openjdk/amber-docs/blob/master/eg-drafts/deconstruction-patterns-records-and-classes.md
> |
> https://github.com/openjdk/amber-docs/blob/master/eg-drafts/deconstruction-patterns-records-and-classes.md
> ]

> This document outlines the semantics of deconstruction patterns and nested
> patterns, and declaration of deconstructors in classes.
In the code: 
public deconstructor B(int a, int b) { 
super(var aa) = this; 
a = aa; 
b = this.b; 
} 
i believe the first line should be 
A(var aa) = super; 

I know that you have consider something like this, but i prefer making the deconstructor a method returning a tuple at Java level, to be closer to the JVM level. 
So a syntax more like 
class Point { 
int x; 
int y; 

(int x, int y) deconstructor { 
return (this.x, this.y); 
} 
} 

Conceptually, it's also more like the reverse of a constructor, a constructor takes the values from the stack to move them to the heap, a desconstructor takes the value from the heap and move them to the stack. 

> (There are some teasers for related features, mostly to put these in context,
> but I don't want to get distracted on those features until these are nailed
> down, so take them as merely context.)
Rémi 
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