HH\Set::lazy

Returns a lazy, access elements only when needed view of the current Set

public function lazy(): HH\Rx\KeyedIterable<arraykey, Tv>;

Normally, memory is allocated for all of the elements of the Set. With a lazy view, memory is allocated for an element only when needed or used in a calculation like in map() or filter().

Guide

• Examples

Returns

• HH\Rx\KeyedIterable<arraykey, Tv> - an KeyedIterable representing the lazy view into the current Set, where the keys are the same as the values.

Examples

This example shows you how to use lazy() on a rather large Set and the time for both a strict and non-strict version. Since we only need 5 of the elements in the end, the lazy view actually allows us to stop after we meet our required 5 without having to actually filter and allocate all 1000000 elements up front.

$set = new Set(range(0, 1000000));

$s = microtime(true);
$non_lazy = $set->filter($x ==> $x % 2 === 0)->take(5);
$e = microtime(true);

var_dump($non_lazy);
echo "Time non-lazy: ".strval($e - $s).PHP_EOL;

// Using a lazy view of the Set can save us a bunch of time, possibly even
// cutting this call time by 90%.
$s = microtime(true);
$lazy = $set->lazy()->filter($x ==> $x % 2 === 0)->take(5);
$e = microtime(true);

var_dump($lazy->toSet());
echo "Time lazy: ".strval($e - $s).PHP_EOL;

object(HH\Set)#4 (5) {
  int(0)
  int(2)
  int(4)
  int(6)
  int(8)
}
Time non-lazy: 0.3235170841217
object(HH\Set)#9 (5) {
  int(0)
  int(2)
  int(4)
  int(6)
  int(8)
}
Time lazy: 0.015014886856079