Re: features for groovy-6.0.0-alpha-1

Hi Paul,

what is "Path A keeps the Stream lazy and propagates onClose -- the 
killer demo for the streaming contract." supposed to mean ?

Cheers,
mg

Am 27.04.2026 um 13:39 schrieb Paul King:
> Hi folks,
>
> I believe the following features are ready for inclusion in Groovy 
> 6.0.0-alpha-1.
> Please see the relevant PRs and Jira issues for more information.
>
> Feedback, as always, is welcome.
>
> Cheers, Paul.
>
> GEP-18 -- Ported GPars features
> ================================
>
> 1. Parallel collections inside a scope -- drop-in speedup
>
>     ParallelScope.withPool(Pool.cpu()) {
>         urls.collectParallel { fetch(it) }
>             .findAllParallel { it.status == 200 }
>             .groupByParallel { it.host }
>     }
>
>    Familiar GPars xxxParallel names, pool-isolated and
>    virtual-thread-ready.
>
> 2. Dataflows -- orchestration by data dependency, not thread
>    choreography
>
>     def df = new Dataflows()
>     async { df.result = combine(df.user, df.prefs) }
>     async { df.user  = loadUser(id) }
>     async { df.prefs = loadPrefs(id) }
>     println await(df.result)
>
>    The order in source is irrelevant; readers block until the
>    writers bind. Reads as plainly as sequential code.
>
> But also, actors/active objects, agents and channels.
>
> GEP-20 -- Additional multi-assignment forms
> ============================================
>
> 1. Tail rest against a Stream -- head/body split with no
>    materialisation
>
>     Files.lines(path).withCloseable { src ->
>         def (header, *body) = src
>         body.filter { !it.isBlank() }.forEach { process(it) }
>     }
>
>    Path A keeps the Stream lazy and propagates onClose -- the
>    killer demo for the streaming contract.
>
> 2. Head and middle rest -- edge-aware slicing in one line
>
>     def (first, *middle, last) = readings    // peel both ends
>     def (l, *m, r)             = segment     // boundary + interior
>
>    Replaces [0] / [1..-2] / [-1] boilerplate that's surprisingly
>    common.
>
> 3. Map-style destructuring -- beans and config in one shot
>
>     def (host: h, port: p, name: n) = config
>     def (name: String fullName, age: int a) = person
>
>    Works against Map, beans, and GroovyObject uniformly via the
>    MOP -- the rename form (name: fullName) is a quiet bonus.
>
>
> When assessing GEP-20, bear in mind the very early draft for GEP-19 
> targetted tentatively for Groovy 7.
>
> GEP-19 -- Structural pattern matching in switch
> ================================================
>
> 1. Recursive list algorithm in its canonical functional shape
>
>     def sum(xs) {
>         switch (xs) {
>             case []                -> 0
>             case [var h, var... t] -> h + sum(t)
>         }
>     }
>
>    The motivating example -- what you can't write tidily today.
>
> 2. Map patterns for tagged-shape dispatch (events, JSON, configs)
>
>     switch (event) {
>         case [type: 'click',  x: var x, y: var y] -> handleClick(x, y)
>         case [type: 'key',    code: var k]        -> handleKey(k)
>         case [type: 'scroll', ...]                -> redraw()
>     }
>
>    Open semantics plus rest binding makes this read like a
>    protocol spec.
>
> 3. Type pattern + record pattern + guard -- visitor replacement
>
>     switch (shape) {
>         case Circle c when c.radius > 0 -> Math.PI * c.radius**2
>         case Rect(int w, int h)         -> w * h
>         case Line(_, Point p2)          -> "ends at $p2"
>         default                         -> 0
>     }
>
>    One construct subsumes instanceof chains, accessor calls, and
>    the constraint check.