Defer processing elements in Sequences

DeferTest.class.php

<?php namespace util\data\unittest;

use util\data\Sequence;

class DeferTest extends \unittest\TestCase {

  #[@test]
  public function defer_using_existing_apis() {
    $deferred= [];
    $result= Sequence::concat(
      Sequence::of([1, 2, 3, 4])
        ->filter(function($i) use(&$deferred) {
          if ($i % 2) {
            return true;
          } else {
            $deferred[]= $i;
            return false;
          }
        }),
        function() use(&$deferred) { return $deferred; }
      )
      ->map(function($i) { return 2 * $i; })
    ;

    $this->assertEquals([2, 6, 4, 8], $result->toArray());
  }

  #[@test]
  public function defer_using_process() {
    $result= Sequence::of([1, 2, 3, 4])
      ->process(function($i) {
        if ($i % 2) {
          return;
        } else {

          // Defer: Skip now, pass on later
          // Retry: Skip now, call process() again
          return Processing::defer($i);
        }
      })
      ->map(function($i) { return 2 * $i; })
    ;

    $this->assertEquals([2, 6, 4, 8], $result->toArray());
  }
}