Call for feedback -- switch expressions in JDK 12
Manoj Palat
manoj.palat at in.ibm.com
Fri Apr 26 04:28:22 UTC 2019
Hi,
One more item in the feedback list:
We understand that the "->" in switch expressions lends itself to future
pattern matching constructs, but is there a real need for "->" to be there
in switch statements as well other than the convenience factor of avoiding
break ( or rather making the break implicit) in switch statements?
Regards,
Manoj
From: "Manoj Palat" <manoj.palat at in.ibm.com>
To: "Alex Buckley" <alex.buckley at oracle.com>
Cc: Stephan Herrmann <stephan.herrmann at berlin.de>,
jdk-dev at openjdk.java.net
Date: 04/19/2019 03:28 AM
Subject: Re: Call for feedback -- switch expressions in JDK 12
Sent by: "jdk-dev" <jdk-dev-bounces at openjdk.java.net>
Hi Alex,
Please find our feedback from Eclipse Java Dev.
1) For the break expression part we would be happy to have the
“overloading” of break replaced by something else ? since this is
already in the cards, no additional comment on this part.
2) Thanks to Remi Forax raising a bug in ecj [
https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.eclipse.org_bugs_show-5Fbug.cgi-3Fid-3D545716&d=DwIFJg&c=jf_iaSHvJObTbx-siA1ZOg&r=A51zLdywEjS50U7u2UMWvsDIrUGEJ5IDXskL5MxIEjA&m=kii1fGYS4Td8yanneEhpKyvY68-2ZuWy6UGnDArvEtU&s=bTz3kPNJIWSaFf9MBqxF1ZKUwUHxpH0AJkS2Noth9O0&e=
] and the
following discussions, we believe that there could be a bug [in spec,
javac as well as ecj] ? see this comment from Stephan Herrmann
https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.eclipse.org_bugs_show-5Fbug.cgi-3Fid-3D545716-23c16&d=DwIFJg&c=jf_iaSHvJObTbx-siA1ZOg&r=A51zLdywEjS50U7u2UMWvsDIrUGEJ5IDXskL5MxIEjA&m=kii1fGYS4Td8yanneEhpKyvY68-2ZuWy6UGnDArvEtU&s=lp0V33xF-hHx6PbOuSpmziGYZGad42PPROmWzFvu8xQ&e=
specifically
for the findings. [@Alex: I am taking the liberty of pointing to the
bug link rather than summarizing here since you have mentioned that a
blog pointer should also be fine]
Regards,
Manoj
Eclipse Java Dev, IBM
From: Alex Buckley <alex.buckley at oracle.com>
To: jdk-dev at openjdk.java.net
Date: 04/17/2019 11:23 PM
Subject: Re: Call for feedback -- switch expressions in JDK 12
Sent by: "jdk-dev" <jdk-dev-bounces at openjdk.java.net>
The feedback we're looking for is "I tried switch expressions in my code
and observed ...". For example:
https://urldefense.proofpoint.com/v2/url?u=https-3A__mail.openjdk.java.net_pipermail_amber-2Ddev_2019-2DMarch_004199.html&d=DwIFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=A51zLdywEjS50U7u2UMWvsDIrUGEJ5IDXskL5MxIEjA&m=yINx0-noxNSSsm-dLx2P9YD7dvF6187FW7CStT07mp4&s=9at0fZB0bQpeEPI5L2IWbMSlUqcdgEsfF5944Rfjaxo&e=
If anyone is blogging about their experience with switch expressions,
feel free to share the URL here. For example, here's a great writeup of
using switch expressions in lambdas:
https://urldefense.proofpoint.com/v2/url?u=http-3A__minborgsjavapot.blogspot.com_2019_03_java-2D12-2Dmapping-2Dwith-2Dswitch-2Dexpressions.html&d=DwIFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=A51zLdywEjS50U7u2UMWvsDIrUGEJ5IDXskL5MxIEjA&m=yINx0-noxNSSsm-dLx2P9YD7dvF6187FW7CStT07mp4&s=JE0ESlf3gLQJ5-QzuOU1uR_xMLngiysxuz0o948ZlW4&e=
Alex
On 4/16/2019 8:24 PM, Netroby wrote:
> int numLetters = switch (day) {
> case MONDAY, FRIDAY, SUNDAY -> 6,
> case TUESDAY -> 7,
> case THURSDAY, SATURDAY -> 8,
> case WEDNESDAY -> 9,
> _ -> 0,
> };
>
> Should we using comma , instead of ;
>
> comma , means these cases the same switch.
>
> Another point, should we have an default match pattern ? using _ or
default
>
>
> idea from rust match
> ```rust
> fn main() {
> let number = 13;
> // TODO ^ Try different values for `number`
>
> println!("Tell me about {}", number);
> match number {
> // Match a single value
> 1 => println!("One!"),
> // Match several values
> 2 | 3 | 5 | 7 | 11 => println!("This is a prime"),
> // Match an inclusive range
> 13...19 => println!("A teen"),
> // Handle the rest of cases
> _ => println!("Ain't special"),
> }
>
> let boolean = true;
> // Match is an expression too
> let binary = match boolean {
> // The arms of a match must cover all the possible values
> false => 0,
> true => 1,
> // TODO ^ Try commenting out one of these arms
> };
>
> println!("{} -> {}", boolean, binary);
> }
>
> ```
>
> Appreciate your time.
> ----------------------------
> Netroby
>
> Alex Buckley <alex.buckley at oracle.com> 于2019年4月17日周三 上午10:00写
道：
>>
>> An easy way to help move Java forward is to try out new features on real
>> code and share your experiences. We're asking for feedback on how you
>> use switch expressions, the new language feature in JDK 12:
>>
>> int numLetters = switch (day) {
>> case MONDAY, FRIDAY, SUNDAY -> 6;
>> case TUESDAY -> 7;
>> case THURSDAY, SATURDAY -> 8;
>> case WEDNESDAY -> 9;
>> };
>>
>> // Multiple labels per case (also allowed in switch statements)
>> // No fallthrough with the -> form (also allowed in switch
statements)
>>
>> Do you find switch expressions useful? Is anything surprising? Did you
>> turn any switch statements into switch expressions? Please let us know
>> on this list, even if the answer is "Tried it. Works fine."
>>
>> To enable switch expressions in your environment:
>> - IntelliJ IDEA 2019.1
>>
https://urldefense.proofpoint.com/v2/url?u=https-3A__blog.jetbrains.com_idea_2019_02_java-2D12-2Dand-2Dintellij-2Didea_&d=DwIFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=A51zLdywEjS50U7u2UMWvsDIrUGEJ5IDXskL5MxIEjA&m=yINx0-noxNSSsm-dLx2P9YD7dvF6187FW7CStT07mp4&s=-WsqDARpX60gLIBem_6IqycbQFRWL5bzkTNGVV322aU&e=
>> - Eclipse 4.11
https://urldefense.proofpoint.com/v2/url?u=https-3A__www.eclipse.org_eclipse_news_4.11_jdt.php-23Java12&d=DwIFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=A51zLdywEjS50U7u2UMWvsDIrUGEJ5IDXskL5MxIEjA&m=yINx0-noxNSSsm-dLx2P9YD7dvF6187FW7CStT07mp4&s=zClnCpCg04gt1vZS1Zz8j64uam6ZkpnGMVe4M5kCYd0&e=
>> - Apache NetBeans 11.0
>>
https://urldefense.proofpoint.com/v2/url?u=https-3A__cwiki.apache.org_confluence_pages_viewpage.action-3FpageId-3D103091452&d=DwIFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=A51zLdywEjS50U7u2UMWvsDIrUGEJ5IDXskL5MxIEjA&m=yINx0-noxNSSsm-dLx2P9YD7dvF6187FW7CStT07mp4&s=5RLv6qs5qiU3r9dJ8KjnT4aPKRyz8hxXvNN0w5Z6x94&e=
>> - jshell in JDK 12 run with `--enable-preview`
>> - javac in JDK 12 run with `--release 12 --enable-preview`
>>
>> Alex
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