"With" for records

[forax at univ-mlv.fr]

> From: "Brian Goetz" <brian.goetz at oracle.com>
> To: "Remi Forax" <forax at univ-mlv.fr>
> Cc: "amber-spec-experts" <amber-spec-experts at openjdk.java.net>
> Sent: Saturday, June 11, 2022 8:16:26 PM
> Subject: Re: "With" for records

> We also probably want a rule to _prevent_ assignment to any locals *other than*
> the synthetic component locals. Assigning to uplevel locals from within a
> `with` block seems like asking for trouble; the with block is like a transform
> on the component locals.
perhaps any locals other that the synthetic ones and the ones declared inside the block. For example: 

record Couple(int first, int second) { 
Couple withMax() { 
return this with { 
var max = Math.max(first, second); // new local variable, it's ok 
first = max; 
second = max; 
}; 
} 
} 

> However, we may need a story (hope not) for _accessing_ uplevel shadowed locals.
> For example:

> record R(A contents) { }
> record A(B contents) { }
> record B(int contents) { }

> R r = ...
> R rr = r with { contents = contents with { contents = 3 }}

> it is possible that the inner block might want additional information from one
> of the enclosing `contents` variables.
or inside the block we may want to have access to the parameters, like in: 
record Complex(double re, double im) { 
Complex withRe(double re) { 
return this with { re = re_from_outer_scope; } // find a syntax here ! 
} 
} 

we can introduce an intermediary local variable but i wonder if there is a better solution ? 
record Complex(double re, double im) { 
Complex withRe(double re) { 
var re_from_outer_scope = re; 
return this with { re = re_from_outer_scope; } 
} 
} 

and two other related questions about the syntax 
- do we allow to not use curly braces if there is only one assignment 
complex with re = 3 
- or do we allow to avoid the last semicolon if there is only one assignment like in your example 
complex with { re = 3 } 

Rémi 

> On 6/10/2022 11:25 AM, Brian Goetz wrote:

>>> About the declaration of local variables, in Java, there is no hiding/shadowing
>>> between local variables, so a code like this is rejected ? Or do we introduce a
>>> special rule for the hiding of implicit variables ?

>> Yes, we probably do need a special rule for this. The component names are fixed,
>> and collisions are likely, so these synthetic variables will probably have to
>> be allowed to shadow other locals.
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