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From Keith Suderman <suder...@anc.org>
Subject Re: [Poll] About supporting Java-like array
Date Sun, 29 Apr 2018 23:39:36 GMT


> On Apr 29, 2018, at 7:10 PM, mg <mgbiz@arscreat.com> wrote:
> 
> Well tickle my belly and colour me green - I always thought using the "as" form was mandatory
here (based on the examples I saw on the net back then) :-)

Yep me too. Learn something new every day ;) 

- Keith

> 
> That means this is the one case where giving an explicit type is the most concise way
to get what you want ;-)
> 
> I would propose the Groovy compiler issue a warning to change the array initialization
from Java- to Groovy-style then...
> Cheers,
> mg
> 
> 
> 
> -------- Urspr√ľngliche Nachricht --------
> Von: Paul King <paulk@asert.com.au>
> Datum: 30.04.18 00:29 (GMT+01:00)
> An: users@groovy.apache.org
> Betreff: Re: [Poll] About supporting Java-like array
> 
> The preferred Groovy syntax would probably still remain:
> 
> int[] fibs = [1, 1, 2, 3, 5, 8]
> 
> Cheers, Paul.
> 
> On Mon, Apr 30, 2018 at 7:17 AM, MG <mgbiz@arscreat.com <mailto:mgbiz@arscreat.com>>
wrote:
> After thinking about this some more for the last weeks
> +1 with asterisk
> from my side:
> 
> 1) I am always for being as Java compatible as possible (though I see that this might
not be feasible in all cases in the future, due to Java changing at a much faster pace and
with more syntax changes now than before; example: Java considered naming the new "var" keword
"def", which is similar to but not the same as Java-var in Groovy...) 
> 
> 2) I feel  { { } } being interpreted as an array containing an empty closure is confusing,
i.e. not least surprise. I would rather not see it cut it so close with regards to what the
Parrot parser can handle syntax-wise. What do others think ?
> 
> 3) After introducing this syntax extension, what will be considered the "Groovy way"
of initializing an array in the future ? Is it still 
> final int[] a = [ 1, 1, 2, 3, 5, 8 ] as int[]
> or
> final int[] a = { 1, 1, 2, 3, 5, 8 }
> ?
> In the 2nd case I would be worried that the core Groovy syntax becomes all over the place
over time, same as with the new Java lambda syntax (though less pronounced, since using/initializing
arrays is typically rare).
> 
> 4) I am not too worried about the breaking edge cases, because I feel they are quite
rare in practice, the compiler catches them, and they are easy to fix.
> 
> Cheers,
> mg
> 
> 
> 
> 
> On 29.04.2018 15:29, Paul King wrote:
>> +1
>> 
>> For completeness, I added some more details about the breaking changes and workarounds
into the issue - included below for easy reading.
>> 
>> Cheers, Paul.
>> 
>> =================
>> 
>> Groovy currently "promotes" a singleton instance of an object into an array for assignments,
e.g.:
>> 
>> Integer[] nums = 42
>> assert nums instanceof Integer[]
>> assert nums.size() == 1
>> assert nums[0] instanceof Integer
>> 
>> This aligns with how Groovy behaves if you try to call `.each{}` on a non-aggregate.
It treats it like a singleton collection and "iterates" over the one item.
>> 
>> The existing behavior also currently works for singleton Closures:
>> 
>> Closure[] fns0 = { }
>> assert fns0 instanceof Closure[]
>> assert fns0.size() == 1
>> assert fns0[0] instanceof Closure
>> 
>> To add support for Java array notation, we will need to partially disable this behavior.
The proposed change involves smart parsing, e.g. it will distinguish cases which must be an
array and cases which must be a closure but there are some degenerate edge cases which will
become breaking changes.
>> 
>> The case with the empty closure above will no longer work, instead you will get this
behavior, i.e. an empty array is given precedence over an empty closure:
>> 
>> Closure[] fns1 = { }
>> assert fns1 instanceof Closure[]
>> assert fns1.size() == 0
>> 
>> To get the old behavior back you have a couple of options. Firstly, you can provide
the explicit closure argument delimiter:
>> 
>> Closure[] fns2 = { -> } // can't be an array
>> assert fns2 instanceof Closure[]
>> assert fns2.size() == 1
>> assert fns2[0] instanceof Closure
>> 
>> Or don't rely on singleton promotion and explicitly provide also the array curly
braces:
>> 
>> Closure[] fns3 = { { } }
>> assert fns3 instanceof Closure[]
>> assert fns3.size() == 1
>> assert fns3[0] instanceof Closure
>> 
>> Similarly, for the case of the identity closure:
>> 
>> Closure[] fns4 = { it }
>> 
>> Previously this worked but under this proposal will give:
>> 
>> groovy.lang.MissingPropertyException: No such property: it ...
>> 
>> Your options are to add the extra array braces as per above, or use explicit params,
e.g.:
>> 
>> Closure[] fns5 = { it -> it }
>> assert fns5 instanceof Closure[]
>> assert fns5.size() == 1
>> assert fns5[0] instanceof Closure
>> 
>> Alternatively, for this special case you have the following additional option:
>> 
>> Closure[] fns6 = Closure.IDENTITY
>> assert fns6 instanceof Closure[]
>> assert fns6.size() == 1
>> assert fns6[0] instanceof Closure
>> 
>> There are other cases as well, e.g. this code which currently creates a closure array
containing a closure returning the integer 0:
>> 
>> Closure[] fns7 = { 0 }
>> 
>> will no longer be supported and will fail with:
>> 
>> org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object
'0' with class 'java.lang.Integer' to class 'groovy.lang.Closure'
>> The solutions are similar to previously (explicit delimiter):
>> 
>> Closure[] fns8 = { -> 0 }
>> 
>> or (explicit outer array braces):
>> 
>> Closure[] fns9 = { { 0 } }
>> 
>> 
>> On Sun, Apr 29, 2018 at 8:37 PM, Daniel.Sun <sunlan@apache.org <mailto:sunlan@apache.org>>
wrote:
>> Hi all,
>> 
>>      As we all know, Java array is one of features widely applied in Java
>> projects. In order to improve the compatibility with Java(Copy & Paste). The
>> PR[1] will make Groovy support java-like array and make the differences[2]
>> with Java less and less, e.g.
>> 
>> *One-Dimensional array*
>> ```
>> String[] names = {'Jochen', 'Paul', 'Daniel'}
>> ```
>> 
>> *Two-Dimensional array*
>> ```
>> int[][] data = {
>>     {1, 2, 3},
>>     {4, 5, 6},
>>     {7, 8, 9},
>>     new int[] { 10, 11, 12 },
>>     {13, 14, 15}
>> }
>> ```
>> 
>> *Annotation array*
>> ```
>> @PropertySources({
>>     @PropertySource("classpath:1.properties"),
>>     @PropertySource("file:2 <>.properties")
>> })
>> public class Controller {}
>> ```
>> 
>> *More examples*
>> Please see the examples on the PR page[1]
>> 
>> *Known breaking changes*
>> 1. Closure array in the dynamic mode
>> Before
>> ```
>> Closure[] y = { {-> 1 + 1 } }
>> assert y[0].call().call() == 2
>> ```
>> After
>> ```
>> Closure[] y = { {-> 1 + 1 } }
>> assert y[0].call() == 2
>> ```
>> 2. String array in the dynamic mode
>> Before
>> ```
>> String[] a = {}
>> assert 1 == a.length
>> assert a[0].contains('closure')
>> ```
>> After
>> ```
>> String[] a = {}
>> assert 0 == a.length
>> ```
>> 
>> 
>>       If Groovy 3 supports Java-like array, what do you think about the new
>> feature? Do you like it? We need your feedback. Thanks in advance!
>> 
>> [+1] I like it
>> [ 0] Not bad
>> [-1] I don't like it, because...
>> 
>> Cheers,
>> Daniel.Sun
>> [1] https://github.com/apache/groovy/pull/691 <https://github.com/apache/groovy/pull/691>
>> [2] http://groovy-lang.org/differences.html <http://groovy-lang.org/differences.html>
>> 
>> 
>> 
>> 
>> --
>> Sent from: http://groovy.329449.n5.nabble.com/Groovy-Users-f329450.html <http://groovy.329449.n5.nabble.com/Groovy-Users-f329450.html>
>> 
> 
> 

----------------------
Keith Suderman
Research Associate
Department of Computer Science
Vassar College, Poughkeepsie NY
suderman@cs.vassar.edu





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