On 9/5/19 6:14 PM, fo...@univ-mlv.fr wrote:
------------------------------------------------------------------------
*De: *"Brian Goetz" <brian.go...@oracle.com>
*À: *"Tagir Valeev" <amae...@gmail.com>, "Remi Forax"
<fo...@univ-mlv.fr>
*Cc: *"amber-spec-experts" <amber-spec-experts@openjdk.java.net>
*Envoyé: *Jeudi 5 Septembre 2019 23:26:34
*Objet: *Re: Draft JLS spec for records
I don't think so. A compact constructor (or require
initializer, as you propose) could be not the only
constructor. An instance initializer is convenient because
it's added to every constructor, regardless of whether it's
compact or not. So the new thing doesn't supersede the
instance initializer and I see no good reason to explicitly
disable it.
Vicente offered another reason why we might want to prohibit the
instance initializer, if only out of expediency; it complicates
the analysis of which fields are DA on all paths through the
constructor (and therefore, do not need to be automatically
initialized.) If you have a record:
record Foo(int i) {
{ this.i = 0; }
}
then the canonical constructor has to see that `i` is always
initialized by the static init, and therefore should be not
initialized. Worse, if we have:
record Foo(int i) {
{ if (tuesday) this.i = 0; }
}
then we have to issue a compilation error, since we have fields
that are neither DA nor DU at the end of the initializer.
None of this is impossible to do, of course; it's just not clear
whether it's worth it, given the limited utility of instance
initializers in records (because we've already banned instance
fields.)
If we want to fix that with an the analysis, it will have to work on
user-written code mixed with generated code,
it doesn't seem to be a good idea.
right I was thinking about the case:
record R(int i, int j) {
public R { // compact constructor
if (i < 0) {
this.i = -i;
} else {
this.j = j;
}
}
}
which doesn't have instance initializer blocks. The thing is where to
draw between cases where the compiler will just issue an error and cases
in which it will generate the missing initializations. In this
particular case the compiler will have to be very clever and generate:
public R { // compact constructor
if (i < 0) {
this.i = -i;
this.j = j; // automatic code
} else {
this.i = i; // automatic code
this.j = j;
}
}
we can do it, it will be complex though, but do we want to do it? Where
to draw the line?
Thanks,
Vicente
so it's Ok to not support instance initializers in record.
Rémi
