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@ 2016-05-24T18:49:26Z

<?php

function powerSet(Iterator $iterator){
    if(!$iterator->valid()){
        return yield new EmptyIterator();
    }
    $one = $iterator->current();
    $rest = new NoRewindIterator($iterator);
    $rest->next();
    foreach(powerSet($rest) as $set){
        $set = iterator_to_array($set);
        yield new ArrayIterator($set);
        
        // why does this work
        yield (function($set, $one){
            yield from array_merge($set, [$one]);
        })($set, $one);

        // but this doesn't?
        // yield (function($set, $one){
        //     yield from $set;
        //     yield $one;
        // })($set, $one);
    }
}

function baz(){
    yield 1;
    yield 2;
    yield 3;
    yield 4;
}
$sets = powerSet(baz());


foreach($sets as $i => $set){
    echo $i+1 . " {";
    $arr = iterator_to_array($set);
    echo implode(", ", $arr);
    echo "}\n";
}

Output for git.master, git.master_jit, rfc.property-hooks: 1 {} 2 {1} 3 {2} 4 {2, 1} 5 {3} 6 {3, 1} 7 {3, 2} 8 {3, 2, 1} 9 {4} 10 {4, 1} 11 {4, 2} 12 {4, 2, 1} 13 {4, 3} 14 {4, 3, 1} 15 {4, 3, 2} 16 {4, 3, 2, 1}

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2020-03-21 RFC: Is_Literal - declined
2020-12-04 Enumerations - included in PHP 8.1
2018-06-15 Typed Properties v2 - implemented in PHP 7.4
2016-08-12 Object typehint - included in PHP 7.2
2016-08-14 Arrow functions - withdrawn
2016-05-29 array_change_keys() - withdrawn
2016-04-19 Lexical scope support for anonymous classes - suspended
2016-04-17 Functional Interfaces - declined
2016-03-16 Typed Properties - superseded in favor of Typed Properties 2.0
2015-08-27 Callable Prototypes - declined
2015-05-01 Short Closures - declined / withdrawn in favor of Arrow Functions
2015-02-18 Scalar type hints v5 - included in PHP 7
2015-02-14 Union Types - declined
2013-09-22 Anonymous classes - included in PHP 7

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