Call for feedback -- switch expressions in JDK 12
Brian Goetz
brian.goetz at oracle.com
Sat Apr 27 22:56:06 UTC 2019
I’m not sure whether you’re asking about the specific overloading of -> (some people find it disturbing that both switch and lambda use the same punctuation; others see a switch as a sort of “function by parts” and the arrow makes sense to them), or about why there was a need to have a shorthand form at all.
We surely could have done this:
case A: break-with 1;
case B: break-with 2;
…
And that might have been a reasonable idea, though people seem to have such an allergy to “break” in switch that the convenience factor was significant.
> 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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