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From MG <>
Subject Re: Possible New Groovy Features...
Date Mon, 21 Aug 2017 20:59:49 GMT
Hi Paul,

thanks for your reply. If I had known you were gonna hit back with so 
much detail, I would have gone with splitting my mail into multiple 
parts (but didn't want to spam the mailing list) ;-)
I will read up on your links and reply in smaller chunks...


On 21.08.2017 04:30, Paul King wrote:
> Hi Markus,
> Thanks for your suggestions. Some neat ideas in your suggestions! Just 
> a general comment to start off with...
> With language design, it's often the details which are important, so 
> I'd suggest rather than going straight from this email to a bunch of 
> PRs, you'd create separate Jira issues for those items you want to 
> pursue and flesh out the design a little more - it's often the dealing 
> with backwards compatibility and handling error situations that take 
> up more of the design time than the actual feature itself. Having said 
> that, please don't be put off with the extra work. We usually follow 
> the same process ourselves and find the extra discipline helps all 
> round. For simple non-controversial enhancements, not much detail 
> might be needed but in other cases, there might be lots of details 
> that need to be handled that might not be apparent at first - plus a 
> Jira issue is a good place for us to suggest hints on how to get started.
> Some more comments inline below ...
> Cheers, Paul.
> On Mon, Aug 21, 2017 at 6:25 AM, MG < 
> <>> wrote:
>     Hi,
>     before I create change requests, I wanted to ask for some quick
>     feedback on the following potential new Groovy features (I
>     apologize beforehand, if any of these are already covered in some
>     way, and I missed it, or if they have been discussed before, etc -
>     just throwing ideas that I find useful out there :-) ):
>      1. Named Parameters: I already posted that feature request here.
>         The most plain vanilla support (support the <name>:<value>,
>         <name>:<value>, ... syntax to give named ctor/method args)
>         would already cover 99% of applications here, I think. The
>         imho most problematic feedback was external libraries without
>         debug information - my question would be how frequently such
>         libraries occur in practice (I personally have never pressed
>         Ctrl+B in IntelliJ and not gotten a method decompile result
>         with parameter names) ?
> It is certainly worth fleshing this out a little more. Such support 
> has been considered in the past [1,2] but that was prior to 
> JEP118[3,4] being finalized and we decided to wait. Some of the 
> backwards compatibility issues mentioned in that thread still remain 
> and we'd need to spell out what we are planning in that regard (that 
> affects what version this might be merged into).  I'll also note that 
> there are some tricks that IDEs might use (looking at source code, 
> javadoc etc.) that we would not likely pursue. There are also some pre 
> java8 tricks that can be used [5,6,7] but I think we would more likely 
> want to pursue the JEP118 approach - though do feel free to experiment 
> if you think those approaches might be useful - we'd need to weigh up 
> what additional libraries that might required to be available for 
> basic compilation. I have less optimism about whether JEP118 metadata 
> information will be available anytime soon - doesn't mean we shouldn't 
> provide support in the meantime for the situations where it does 
> exist. I did a sample size of 1 by downloading the latest Guava and it 
> wasn't available in that library - also the Java libraries themselves 
> didn't have that information last time I checked. Also, there is an 
> old issue that could be useful that would work for constructors even 
> on old JDK versions using a JavaBean annotation[8] though again I 
> don't think widely used. Also, we'd need to understand if there are 
> any impacts on Groovy's mixed Map/positional notation and whether true 
> optional arguments support would be included[9].
> [1]!topic/groovy-user/8MuO1TTw-aQ 
> <>
> [2] 
> <>
> [3] <>
> [4] 
> <>
> [5] 
> <>
> [6] 

> <>
> [7] 

> <>
> [8] 
> <>
> [9] 
> <>
>      1. Support making all method/ctor parameters final by default
>         through "autofinal" Groovy compiler flag:
>         Foo(int x, String s) { // final keyword is auto added to all
>         parameters, if compiler flag is set, i.e. this automatically
>         becomes Foo(final int x, final String s)
>         this.x = x; this.s
>         }
>         Rationale: Even if Groovy source samples use def instead of
>         final a lot, parameters (and variables) are, according to my
>         experience, most of the time actually final in practice (In
>         the few cases where one needs to modify a parameter, it can
>         immediately be assigned to a variable). This feature would
>         reduce the source code clutter that comes from the need to
>         qualify parameters as final all the time.
> You can already leave off the "clutter" and apply a CodeNarc rule[1] 
> to detect "bad" style. Also, it would be an easy task to create an 
> @AutoFinal local transform which could then be automatically applied 
> using a compiler customizer. I think going further with a dedicated 
> compiler flag would be a later step if such a local transform became 
> extremely popular.
> [1] 

> <>
>      1. Deduce the type of final fields from their assigned value:
>      2. class Foo {
>         final device = new PrinterDevice(...) // device field will
>         have type PrinterDevice instead of Object when reflection is
>         used on class Foo
>         }
>         Rationale: While IntelliJ does a good job at deducing the type
>         of final fields, it would still be better if the Groovy
>         language itself would use the more specialized type here, for
>         e.g. reflection purposes
> With @Typechecked or @CompileStatic type inferencing is going to be in 
> play. During debugging the runtime type is going to be available. What 
> "reflective purposes" did you have in mind?
>      1. Introduce a "var" (o.s.) keyword that allows deduction of type
>         through assignment:
>         var device = new PrinterDevice(...) // device variable will
>         have type PrinterDevice without the need to explictely state that
>         Rationale: This is a well known feature of other languages,
>         that reduces the need to explictely define the type of variables.
> How is this different to the current type inferencing?
>      1. Always allow ctor calls without new keyword:
>         final foo = Foo("abc") // creates a new Foo instance by
>         calling Foo class ctor with signature
>         Rationale: new keyword was necessary in C++ to distinguish
>         heap vs stack variable allocation. No such need exists in
>         Groovy, so the keyword just clutters the source code. Naming
>         convention of method names being always lowercase prevents
>         name clashes with methods.
>  A partial solution to this is available via @Newify. As far as I 
> know, @Newify hasn't been super popular, so we'd need to think 
> carefully about introducing this.
>      1. "Variable plus Name" support: One of the most useful macros I
>         used in C++ was NV(x), where I passed a variable, and created
>         a NamedVariable instance, which was automatically passed the
>         name and the value of the variable (through simple macro
>         stringify). I would love to see something similar in Groovy.
>         Rationale: Most important application is DRY creation of debug
>         output, e.g.:  println NV(longVariableName)  // equivalent
>         result to println "longVariableName=$longVariableName" avoding
>         the potential classical copy & paste error
>         "longVariableName=$longrVariableName"
> Sounds like a possible candidate for using Macros?
>      1. Support break/continue to work as if a closure was a block
>         construct, e.g. through an annotation on the Closure parameter:
>         sqe.forEachRow("select * from PERSON") { final row ->
>         if(row.TAG == 0) { continue } // Move to next iteration in
>         forEachRow iteration over PERSON table
>         if(row.TAG == 1) { break } // Return form closure & return
>         from forEachRow (effectively stopping to iterate over PERSON
>         table rows, continuing after the method call)
>         }
>         Rationale: Groovy's support for giving a Closure as the last
>         argument outside of the parameter brackets is one of its most
>         neat features. Supporting break/continue with expected (least
>         surprise) semantics inside of such closures, would make this
>         feature complete.
>         (Note: I have implemented support for a "BreakLoopException"
>         in my code, so that the closure body can signal a break to
>         e.g. forEachRow, but that is still quite an akward solution,
>         that breaks the illusion that forEachRow works like a regular
>         for-each statement)
> Non-local transfers (break/continue/non-local returns) have been 
> discussed before[1] but perhaps worth revisiting now that Scala 
> supports the non-local return approach using Exceptions[2] and Kotlin 
> has labelled returns in lambda functions[3]. The main issue to keep in 
> mind would be backwards compatibility/breaking changes.
> [1] 
> <>
> [2] 
> <>
> [3] 
> <>
>      1. CompileStatic byte code call compatibility with Java: I have
>         included this, since I saw it on the mailing list here, and I
>         always tell everyone that Groovy is basically a drop in
>         replacement for Java, which in this case, if obfuscation is
>         part of the game, does not seem to be the case (in addition my
>         son has also started to mod Minecraft a bit, and I wanted to
>         use this to introduce him to Groovy - after he has suffered
>         through a bit of Java ;-) ).
> There are definitely edge cases where @CompileStatic falls back to 
> dynamic calls which we want to improve.
>     mg

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