There is a pattern match syntax that is implemented using Groovy
macros so that you can use the match "keyword".
https://github.com/bsideup/groovy-pattern-match/blob/feature/dsl-like-matching/src/test/groovy/ru/trylogic/groovy/pattern/PatternMatchingMacroMethodsTest.groovy
The current version is more DSL-like using "when", "then" and "orElse"
instead of operators.
There was an earlier version that used case as "when", | as "or" and
>> as "then".
https://github.com/bsideup/groovy-pattern-match/blob/master/src/test/groovy/ru/trylogic/groovy/pattern/PatternMatchingMacroMethodsTest.groovy
In terms of what Groovy supports right now, you can use closures for
each case in a switch statement and check anything you want about the
expression supplied to the switch or the context around the switch
statement.
I agree with Paul that supporting Java's switch expression
enhancements would cover a lot of common cases. Then we could regroup
and see what sort of edge cases remain and if there is merit in adding
something to help with them.
*From:* MG <[email protected]>
*Sent:* Friday, August 7, 2020 12:41 PM
*To:* [email protected]; Paul King <[email protected]>
*Subject:* switch destructuring
Hi Paul,
the Python destructuring sure looks powerful (I did my master thesis
in Mathematica, which is all about pattern matching).
Here is one of the Python examples in a potential Groovy syntax, which
tries to convert its argument into a 3D-point:
@Newify(pattern=/[A-Z][A-Za-z0-9_]+/)
Point3d makePoint3d(final point3dCandidate) {
match(point3dCandidate) {
case [Number x, Number y]:
return Point3d(x, y, 0)
case [Number x, Number y, Number z]:
return Point3d(x, y, z)
case Point2d(x, y):
return Point3d(x, y, 0)
case Point3d(_, _, _):
return point3dCandidate
default:
throw TypeError("${NV(point3dCanditate) could not be
converted to Point3D")
}
}
Cheers,
mg
On 07/08/2020 12:53, Paul King wrote:
I created a starting set of NV, NVI and NVD macros similar (but
slightly different) to what mg has described previously. I see
that as a starting point for discussion.
Something like 'returnIf' wouldn't be hard to add but I'd
personally prefer to explore enhancing our switch statement first
since I think that would cover many use cases where I'd be tempted
to try 'returnIf'.
Just on switch statements we have Java 13/14 enhanced switch we
could explore (switch expressions, yields/no breaks) and
destructuring like python's latest proposal[1] but obviously with
our own syntax.
Cheers, Paul.
[1] https://www.python.org/dev/peps/pep-0622/
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On Wed, Aug 5, 2020 at 7:53 AM MG <[email protected]
<mailto:[email protected]>> wrote:
Hi Eric,
yea, I got that, that's why I said "In that case a global
setting might /also/ be useful".
But I doubt that the majority of Groovy users out there who
want to quickly check if it is macros that make their code
break in Groovy 4 would know that to do so they just need to
"add the macro transform class to the disallowed list in
CompilerConfiguration"; to be able to do so would mean one
would a) need to know the macro transform class exists and
what its purpose and exact name is, b) how the disallowed list
in CompilerConfiguration works (that's the easy part), as well
as last but not least c) to be sure that doing so will not
just break part or all of Groovy... ;-)
I think you grossly underestimate the amount of Groovy
(internal) knowledge you have :-)
Cheers,
mg
On 04/08/2020 18:27, Milles, Eric (TR Technology) wrote:
In terms of globally disabling macro methods, you can just
add the macro transform class to the disallowed list in
CompilerConfiguration. I think Paul is describing a
mechanism where an individual macro method is taken out of
service.
*From:* MG <[email protected]> <mailto:[email protected]>
*Sent:* Tuesday, August 4, 2020 9:53 AM
*To:* [email protected]
<mailto:[email protected]>; Paul King
<[email protected]> <mailto:[email protected]>
*Subject:* Re: [PROPOSAL]Support conditional return
Hi Paul,
thanks for clearing that up :-)
@unforeseen implications: In that case a global
-Dgroovy.macro.enable=false
might also be useful, to do a quick check if it is macros
that are causing the problem (if we do not have that already).
Btw: Do we have a way to hide the macro definitions from
e.g. IntelliJ Intellisense, and only show the stub
implementation ? I use the NV macros* extensively by now
in my code, and what I found is, that always having to
select and import the stub class, and not the macro class
is a (small) hassle.
Cheers,
mg
*In practice it turns out the NV variety I use the most is
NVL, which returns a list of NV instances, so is good for
logging multiple variables. At some point in the future
there will need to be a discussion what varieties we want
to support; my suggestion would be:
NV(x) ... single NameAndValue class instance
NVL(x0,x1,...) ... list of NameAndValue instances
NVS(x0,x1,...) ... "x0=$x0, x1=$x1, ..."-GString
(we could also have NVS return an (efficiently built)
String, and NVGS return the GString, but I am not sure
whether that it is worth it)
On 04/08/2020 08:17, Paul King wrote:
Hi mg,
Just on supplying our own macros, we should do this
for Groovy 4. We have been reluctant so far because we
have been conservative about unforeseen implications.
However, unless we start using them more widely, we
aren't going to learn those implications.
I'd suggest having them (to start with) in their own
optional incubating module (e.g. groovy-macro-samples)
and we should come up with a way to disable any one of
them, e.g.
-Dgroovy.macro.enable.returnIf=false
-Dgroovy.macro.enable.NV=true (or whatever).
Cheers, Paul.
On Wed, Jul 29, 2020 at 10:07 AM MG
<[email protected] <mailto:[email protected]>> wrote:
I like that idea :-)
(unless someone has a really convincing argument
why not, 100% for
sticking with "it" instead of "_"/"$")
That would also allow for more flexibility with
e.g. regards to the
number of methods that are being evaluated,
without getting into the
problematic area of whether/ how to support this
syntax-wise.
If there is nothing blocking this, the question is
if Groovy should
supply a basic version of such a macro (if Groovy
is ever planning to
supply macros of its own) ?
Cheers,
mg
On 28/07/2020 16:08, Milles, Eric (TR Technology)
wrote:
> If switch expression or pattern match macro is
insufficient, could a macro be written to cover
this "conditional return"?
>
> // "it" could easily be replaced by "_" or "$"
as mentioned previously as options
> def doSomething(int a) {
> returnIf(callB(), a > 6 && it > 10)
> returnIf(callC(), a > 5 && it > 20)
> returnIf(callD(), a > 4 && it > 30)
> }
>
> vs.
>
> def doSomething(int a) {
> return callB() if (a > 6 && _ > 10)
> return callC() if (a > 5 && _ > 20)
> return callD() if (a > 4 && _ > 30)
> }
>
> -----Original Message-----
> From: Daniel Sun <[email protected]
<mailto:[email protected]>>
> Sent: Sunday, July 26, 2020 6:23 PM
> To: [email protected]
<mailto:[email protected]>
> Subject: Re: [PROPOSAL]Support conditional return
>
> Hi Sergei,
>
> ( Copied from twitter:
https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftwitter.com%2Fbsideup%2Fstatus%2F1287477595643289601%3Fs%3D20&data=02%7C01%7Ceric.milles%40thomsonreuters.com%7C411c66fda05844d7429908d831bacc9d%7C62ccb8646a1a4b5d8e1c397dec1a8258%7C0%7C0%7C637314025668554080&sdata=vNa3dz0H%2BJAegS9Zb8HW2by0ueceqCKI6qDVFpBpbc4%3D&reserved=0
<https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftwitter.com%2Fbsideup%2Fstatus%2F1287477595643289601%3Fs%3D20&data=02%7C01%7Ceric.milles%40thomsonreuters.com%7C47e9eafa50324d20595008d83af90b06%7C62ccb8646a1a4b5d8e1c397dec1a8258%7C0%7C0%7C637324188604137339&sdata=fUiBY%2F%2F%2BbzeUKMslv4iGJJEa8MHLnS%2BAH%2BNwyhlqVhQ%3D&reserved=0>
)
>> But isn't it better with pattern matching? And
what is "_" here?
> The underscore represents the return value
>
>> Anyways:
>> ```
>> return match (_) {
>> case { it < 5 }: callC();
>> case { it > 10 }: callB();
>> case { it != null }: callA();
>> default: {
>> LOG.debug "returning callD"
>> return callD()
>> }
>> }
>> ```
> pattern matching may cover some cases of
Conditional Return, but it can not cover all.
Actually the Conditional Return is more flexible, e.g.
>
> ```
> def chooseMethod(String methodName, Object[]
arguments) {
> return doChooseMethod(methodName, arguments)
if _ != null
>
> for (Class type : [Character.TYPE,
Integer.TYPE]) {
> return doChooseMethod(methodName,
adjustArguments(arguments.clone(), type)) if _ != null
> }
>
> throw new
GroovyRuntimeException("$methodName not found") } ```
>
> Even we could simplify the above code with
`return?` if the condition is Groovy truth:
> ```
> def chooseMethod(String methodName, Object[]
arguments) {
> return? doChooseMethod(methodName, arguments)
>
> for (Class type : [Character.TYPE,
Integer.TYPE]) {
> return? doChooseMethod(methodName,
adjustArguments(arguments.clone(), type))
> }
>
> throw new
GroovyRuntimeException("$methodName not found") } ```
>
> Cheers,
> Daniel Sun
> On 2020/07/26 18:23:41, Daniel Sun
<[email protected] <mailto:[email protected]>> wrote:
>> Hi mg,
>>
>>> maybe you can give some real life code where
you encounter this on a regular basis ?
>> Let's think about the case about choosing
method by method name and arguments:
>>
>> ```
>> def chooseMethod(String methodName, Object[]
arguments) {
>> def methodChosen =
doChooseMethod(methodName, arguments)
>> if (null != methodChosen) return methodChosen
>>
>> methodChosen = doChooseMethod(methodName,
adjustArguments(arguments.clone(), Character.TYPE))
>> if (null != methodChosen) return methodChosen
>>
>> methodChosen = doChooseMethod(methodName,
adjustArguments(arguments.clone(), Integer.TYPE))
>> if (null != methodChosen) return methodChosen
>>
>> throw new
GroovyRuntimeException("$methodName not found") } ```
>>
>> The above code could be simplified as:
>> ```
>> def chooseMethod(String methodName, Object[]
arguments) {
>> return? doChooseMethod(methodName, arguments)
>>
>> return? doChooseMethod(methodName,
>> adjustArguments(arguments.clone(), Character.TYPE))
>>
>> return? doChooseMethod(methodName,
>> adjustArguments(arguments.clone(), Integer.TYPE))
>>
>> throw new
GroovyRuntimeException("$methodName not found") } ```
>>
>> Or a general version:
>> ```
>> def chooseMethod(String methodName, Object[]
arguments) {
>> return doChooseMethod(methodName,
arguments) if _ != null
>>
>> return doChooseMethod(methodName,
>> adjustArguments(arguments.clone(),
Character.TYPE)) if _ != null
>>
>> return doChooseMethod(methodName,
>> adjustArguments(arguments.clone(),
Integer.TYPE)) if _ != null
>>
>> throw new
GroovyRuntimeException("$methodName not found") } ```
>>
>>
>> Cheers,
>> Daniel Sun
>> On 2020/07/26 17:11:07, MG <[email protected]
<mailto:[email protected]>> wrote:
>>> Hi Daniel,
>>>
>>> currently I would be +/- 0 on this.
>>>
>>> Thoughts:
>>>
>>> 1. I feel I have written this before, but I
myself do not encounter the
>>> situation where I would need to return
the result of a method call
>>> only if it meets certain conditions when
programming (maybe you can
>>> give some real life code where you
encounter this on a regular basis ?).
>>> 2. If I have more than one return, it
typcially is an early out, which
>>> depends on the method's input parameters,
not on the result of
>>> another method call.
>>> 3. Since I do a lot of logging / log
debugging, I typically assign the
>>> return value to a variable, so I can
debug-log it before the one
>>> return of the method.
>>> 4. In fact I have had to refactor code
written by other people from
>>> multi-return methods to single return, to
be able to track down bugs.
>>>
>>> So overall I am not sure one should enable
people to make it easier
>>> to write non-single-return methods ;-)
>>>
>>>
>>> Purely syntax wise I would prefer
>>> return?
>>> for the simple case,
>>>
>>> and
>>>
>>> return <something> if <condition>
>>> for the more complex one*.
>>>
>>> I find
>>> return(<condition) <something>
>>> confusing on what is actually returned.
>>>
>>> Cheers,
>>> mg
>>>
>>> *Though I wonder if people would not then
expect this
>>> if-postfix-syntax to also work for e.g.
assignments and method calls...
>>>
>>>
>>> On 26/07/2020 16:15, Daniel Sun wrote:
>>>> Hi Mario,
>>>>
>>>> I think you have got the point of the
proposal ;-)
>>>>
>>>> If we prefer the verbose but clear
syntax, I think we could introduce `_` to
represent the return value for concise shape:
>>>>
>>>> ```
>>>> return callB() if (_ != null && _ > 10)
>>>>
>>>> // The following code is like lambda
expression, which is a bit
>>>> more verbose return callB() if (result ->
result != null && result
>>>>> 10) ```
>>>> Show the `_` usage in your example:
>>>> ```
>>>> def doSomething(int a) {
>>>> return callB() if (a > 6 && _ > 10)
>>>> return callC() if (a > 5 && _ > 20)
>>>> return callD() if (a > 4 && _ > 30) } ```
>>>>
>>>> ```
>>>> // optional parentheses
>>>> def doSomething(int a) {
>>>> return callB() if a > 6 && _ > 10
>>>> return callC() if a > 5 && _ > 20
>>>> return callD() if a > 4 && _ > 30 } ```
>>>>
>>>> ```
>>>> // one more example
>>>> def doSomething(int a) {
>>>> return callB() if a > 6 && _ > 10
>>>> return callC() + callD() if a > 5 && _ >
50 } ```
>>>>
>>>> BTW, the parentheses behind `if` could
be optional.
>>>>
>>>> Cheers,
>>>> Daniel Sun
>>>> On 2020/07/26 11:29:39, Mario Garcia
<[email protected]
<mailto:[email protected]>> wrote:
>>>>> Hi all:
>>>>>
>>>>> Very interesting topic.
>>>>>
>>>>> The first idea sprang to mind was the PMD
rule in Java saying you
>>>>> should have more than one exit point in your
methods (
>>>>>
https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpmd.github.io%2Flatest%2Fpmd_rules_java_codestyle.html%23onlyonereturn&data=02%7C01%7Ceric.milles%40thomsonreuters.com%7C411c66fda05844d7429908d831bacc9d%7C62ccb8646a1a4b5d8e1c397dec1a8258%7C0%7C0%7C637314025668554080&sdata=5m%2B5ejCWEicseaUp5wK0UDjHwpfMFht5ptjglZ9IWS4%3D&reserved=0
<https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpmd.github.io%2Flatest%2Fpmd_rules_java_codestyle.html%23onlyonereturn&data=02%7C01%7Ceric.milles%40thomsonreuters.com%7C47e9eafa50324d20595008d83af90b06%7C62ccb8646a1a4b5d8e1c397dec1a8258%7C0%7C0%7C637324188604147336&sdata=IvRo8uB78duVVpplmqp290RZA1oyX9TX2XVqg1Wo6R8%3D&reserved=0>).
>>>>> But the reality is that sometimes (more
often than not) we are
>>>>> forced to break that rule. In fact sometimes
we could even argue
>>>>> that breaking that rule makes the code
clearer (e.g
>>>>>
https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2
<https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%252>
>>>>>
Fmedium.com%2Fncr-edinburgh%2Fearly-exit-c86d5f0698ba&data=02
>>>>> %7C01%7Ceric.milles%40thomsonreuters.com
<https://nam02.safelinks.protection.outlook.com/?url=http%3A%2F%2F40thomsonreuters.com%2F&data=02%7C01%7Ceric.milles%40thomsonreuters.com%7C47e9eafa50324d20595008d83af90b06%7C62ccb8646a1a4b5d8e1c397dec1a8258%7C0%7C0%7C637324188604157330&sdata=vJ0EGtfV1DZaAmfH77soyzfRZTfWuYDXm0WRwqeTy1E%3D&reserved=0>%7C411c66fda05844d7429908
>>>>>
d831bacc9d%7C62ccb8646a1a4b5d8e1c397dec1a8258%7C0%7C0%7C637314025
>>>>>
668554080&sdata=q8VrgoQDeH85232oyMgQT8WwljNqoUjIc4cS7GGqH5I%3
>>>>> D&reserved=0)
>>>>>
>>>>> Although my initial reaction was to be
against the proposal,
>>>>> however after doing some coding, I've found
that neither elvis
>>>>> nor ternary operators makes it easier nor
clearer. Here's why I think so. Taking Daniel's
example:
>>>>>
>>>>> ```
>>>>> def m() {
>>>>> def a = callA()
>>>>> if (null != a) return a
>>>>>
>>>>> def b = callB()
>>>>> if (b > 10) return b
>>>>>
>>>>> def c = callC()
>>>>> if (null != c && c < 10) return c
>>>>>
>>>>> LOGGER.debug('the default value will be
returned')
>>>>>
>>>>> return defaultValue
>>>>> }
>>>>> ```
>>>>> The shortest elvis operator approach I could
think of was:
>>>>> ```
>>>>> def m2() {
>>>>> return callA()
>>>>> ?: callB().with { it > 10 ? it : null }
>>>>> ?: callC().with { null != it && it
<10 ? it : null } }
>>>>> ```
>>>>>
>>>>> which to be honest, is ugly to read, whereas
Daniel's proposal is just:
>>>>>
>>>>> ```
>>>>> def m() {
>>>>> return? callA()
>>>>> return(r -> r > 10) callB()
>>>>> return(r -> null != r && r < 10) callC()
>>>>> return defaultValue
>>>>> }
>>>>> ```
>>>>>
>>>>> Once said that, I would say this conditional
return could be
>>>>> useful only when there are more than two
exit points, otherwise
>>>>> ternary or elvis operators may be good enough.
>>>>>
>>>>> So, bottom line, I kinda agree to add
conditional return, but I'm
>>>>> not sure about the final syntax:
>>>>>
>>>>> ```
>>>>> return(r -> r > 10) callB()
>>>>> return callB() [r -> r > 10]
>>>>> return callB() if (r -> r > 10)
>>>>> ```
>>>>>
>>>>> Between the three I the one that I like the
most is the third one:
>>>>>
>>>>> ```
>>>>> return callB() if (r -> r > 10)
>>>>> ```
>>>>>
>>>>> You can read it in plain english as "return
this if this
>>>>> condition happens".
>>>>>
>>>>> Apart from Daniel's use case, using this
option could open the
>>>>> possibility to use, not only a closure or
lambda expression, but
>>>>> also a plain expression. A nice side effect
could be that
>>>>> something like the following code:
>>>>>
>>>>> ```
>>>>> def doSomething(int a) {
>>>>> return callB() if a > 6
>>>>> return callC() if a > 5
>>>>> return callD() if a > 4
>>>>> }
>>>>> ```
>>>>>
>>>>> turns out to be a shorter (and in my opinion
nicest) way of
>>>>> switch case (when you want every branch to
return something):
>>>>>
>>>>> ```
>>>>> def doSomething(int a) {
>>>>> switch (a) {
>>>>> case { it > 6 }: return callB()
>>>>> case { it > 5 }: return callC()
>>>>> case { it > 4 }: return callD()
>>>>> }
>>>>> }
>>>>> ```
>>>>>
>>>>> Well, bottom line, I'm +1 Daniel's proposal
because I've seen
>>>>> some cases where this conditional return
could make the code clearer.
>>>>>
>>>>> Cheers
>>>>> Mario
>>>>>
>>>>> El sáb., 25 jul. 2020 a las 23:55, Paolo Di
Tommaso (<
>>>>> [email protected]
<mailto:[email protected]>>) escribió:
>>>>>
>>>>>> It's not much easier a conditional
expression (or even the elvis
>>>>>> operator)?
>>>>>>
>>>>>> ```
>>>>>> def m() {
>>>>>> def r = callSomeMethod()
>>>>>> return r != null ? r :
theDefaultResult } ```
>>>>>>
>>>>>>
>>>>>> On Sat, Jul 25, 2020 at 8:56 PM Daniel Sun
<[email protected] <mailto:[email protected]>> wrote:
>>>>>>
>>>>>>> Hi all,
>>>>>>>
>>>>>>> We always have to check the
returning value, if it match
>>>>>>> some condition, return it. How about
simplifying it? Let's see an example:
>>>>>>>
>>>>>>> ```
>>>>>>> def m() {
>>>>>>> def r = callSomeMethod()
>>>>>>> if (null != r) return r
>>>>>>>
>>>>>>> return theDefaultResult
>>>>>>> }
>>>>>>> ```
>>>>>>>
>>>>>>> How about simplifying the above code as
follows:
>>>>>>> ```
>>>>>>> def m() {
>>>>>>> return? callSomeMethod()
>>>>>>> return theDefaultResult
>>>>>>> }
>>>>>>> ```
>>>>>>>
>>>>>>> Futhermore, we could make the conditional
return more general:
>>>>>>> ```
>>>>>>> def m() {
>>>>>>> return(r -> r != null) callSomeMethod()
// we could do
>>>>>>> more checking, e.g. r > 10
>>>>>>> return theDefaultResult
>>>>>>> }
>>>>>>> ```
>>>>>>>
>>>>>>> Any thoughts?
>>>>>>>
>>>>>>> Cheers,
>>>>>>> Daniel Sun
>>>>>>>
>>>
