<div dir="ltr"><div dir="ltr">On Mon, Oct 31, 2022 at 3:08 PM Brian Goetz <<a href="mailto:brian.goetz@oracle.com" target="_blank">brian.goetz@oracle.com</a>> wrote:<br></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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I would really like it if we had some warnings to detect more of
the cases where `this` might escape construction, such as
passing `this` explicitly to a method, invoking a non-final
instance method, or invoking an instance method whose
implementation is in a superclass. (Same for use of `this` in
init blocks.) </font></font></div></blockquote><div><br></div><div>Just to say: that would be awesome. Escaping thisses are really confounding to static analysis, because few method bodies can ever be known to be running safely past the construct-initialize gap.</div><div><br></div><div>On the main topic, for whatever it's worth, if more things like this became possible I'm not 100% sure we'd allow them in our codebase anyway. The best practice is still "don't do work in constructors": have a method get all the field values ready so the constructor has only to store them. The reason again is that the construct-init gap is a nasty place for code to live in, where bugs are hard to reliably prevent. Fortunately methods wrapping constructors often serve better as external API for several other reasons anyway.</div><div><br></div><div>That doesn't constitute an argument *against* the feature.</div><div><br></div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div>
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<div>On 10/31/2022 3:18 PM, Archie Cobbs
wrote:<br>
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<div>This is an old thread which I've been looking at again
lately.</div>
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<div>To summarize, the idea is to relax the JLS rules about
code prior to super()/this() invocation to more closely
match what the JVM allows, which is field assignments and
any code that doesn't reference 'this'. Relevant issues are
<a href="https://bugs.openjdk.org/browse/JDK-8194743" target="_blank">JDK-8194743</a> and
<a href="https://bugs.openjdk.org/browse/JDK-8193760" target="_blank">JDK-8193760</a>.<br>
</div>
<div><br>
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<div>In order to make this idea less theoretical, I've
prototyped all the required compiler changes. There is also
a <a href="https://urldefense.com/v3/__https://github.com/archiecobbs/jdk/blob/JDK-8193760/README-JDK-8193760.md__;!!ACWV5N9M2RV99hQ!IFOxLGBuSAtoSNYjvgWAbvbnDuMuHauJA4BIffX89H5Q_c0wG__CXaZEcL6ZG7_e_uQ6KhbytfzaMQ_YMAOcpvY$" target="_blank">write-up describing
them</a>.<br>
</div>
<div><br>
</div>
<div>There are a few interesting subtleties, e.g. relating to
initialization blocks, and there is also a sub-question,
which is whether to allow invoking super()/this() within a
try block (this would have to be under the restriction that
any catch or finally clause must not return normally).
Currently that's not possible without a small JVM change,
which I also think might be worth considering to really
round out this new feature. See the writeup for details.</div>
<div><br>
</div>
<div>To see some examples of what would be allowed, see <a href="https://urldefense.com/v3/__https://github.com/archiecobbs/jdk/blob/JDK-8193760/test/langtools/tools/javac/superInit/SuperInitGood.java__;!!ACWV5N9M2RV99hQ!IFOxLGBuSAtoSNYjvgWAbvbnDuMuHauJA4BIffX89H5Q_c0wG__CXaZEcL6ZG7_e_uQ6KhbytfzaMQ_YIuRHaaQ$" target="_blank">this unit test</a>.
The compiler changes are <a href="https://urldefense.com/v3/__https://github.com/openjdk/jdk/compare/master...archiecobbs:jdk:JDK-8193760__;!!ACWV5N9M2RV99hQ!IFOxLGBuSAtoSNYjvgWAbvbnDuMuHauJA4BIffX89H5Q_c0wG__CXaZEcL6ZG7_e_uQ6KhbytfzaMQ_Y-maJVCk$" target="_blank">here</a>.</div>
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<div>Thoughts?<br>
</div>
<div><br>
</div>
<div>-Archie<br>
</div>
<div><br>
</div>
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<div dir="ltr" class="gmail_attr">On Thu, Jan 17, 2019 at 8:42
AM Brian Goetz <<a href="mailto:brian.goetz@oracle.com" target="_blank">brian.goetz@oracle.com</a>>
wrote:<br>
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<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Some things have improved
for this feature since we last talked; several verifier
issues that this would have pushed on have been resolved.
So it’s moved from the “way too expensive for the benefit”
category into the “there are lots of things we can do, is
this really what we want to spend our effort and complexity
budget on” category. <br>
<br>
My view on this is that while there’s nothing wrong with it,
it’s also a pretty minor wart. If this fell out of a bigger
feature, I’d certainly not object, but I’d rather spend the
effort and complexity budget on things that have broader
benefit.<br>
<br>
> On Jan 16, 2019, at 5:48 PM, Archie Cobbs <<a href="mailto:archie.cobbs@gmail.com" target="_blank">archie.cobbs@gmail.com</a>>
wrote:<br>
> <br>
> I'm curious what are people's current thoughts on
loosening the<br>
> requirements for super() invocation in the context of
Amber, e.g.:<br>
> <br>
> public class MyInputStream extends FilterInputStream
{<br>
> public MyInputStream(InputStream in) {<br>
> if (in == null)<br>
> throw new IllegalArgumentException("null
input");<br>
> super(in); // look ma!<br>
> }<br>
> }<br>
><br clear="all">
</blockquote>
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<br>
-- <br>
<div dir="ltr">Archie L. Cobbs<br>
</div>
</div>
</blockquote>
<br>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div style="line-height:1.5em;padding-top:10px;margin-top:10px;color:rgb(85,85,85);font-family:sans-serif"><span style="border-width:2px 0px 0px;border-style:solid;border-color:rgb(213,15,37);padding-top:2px;margin-top:2px">Kevin Bourrillion |</span><span style="border-width:2px 0px 0px;border-style:solid;border-color:rgb(51,105,232);padding-top:2px;margin-top:2px"> Java Librarian |</span><span style="border-width:2px 0px 0px;border-style:solid;border-color:rgb(0,153,57);padding-top:2px;margin-top:2px"> Google, Inc. |</span><span style="border-width:2px 0px 0px;border-style:solid;border-color:rgb(238,178,17);padding-top:2px;margin-top:2px"> <a href="mailto:kevinb@google.com" target="_blank">kevinb@google.com</a></span></div></div></div></div></div></div></div></div>