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<?php |
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namespace Bdf\Collection\Stream\Accumulator; |
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use Bdf\Collection\Stream\StreamInterface; |
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/** |
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* Base accumulators for perform standard reduce operations on streams |
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* |
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* @see AccumulatorInterface |
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* @see StreamInterface::reduce() |
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*/ |
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final class Accumulators |
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{ |
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/** @var AccumulatorInterface|null */ |
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private static $sum; |
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/** @var AccumulatorInterface|null */ |
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private static $multiply; |
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/** @var AccumulatorInterface|null */ |
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private static $min; |
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/** @var AccumulatorInterface|null */ |
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private static $max; |
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/** Deny instantiation */ |
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private function __construct() { } |
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/** |
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* Perform a sum on each elements of the stream |
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* |
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* <code> |
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* $stream = new ArrayStream([1, 2, 3]); |
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* $stream->reduce(Accumulators::sum()); // 6 |
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* </code> |
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* |
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* @template V as numeric |
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* |
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* @return AccumulatorInterface<V, V> |
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*/ |
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public static function sum() |
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{ |
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if (self::$sum) { |
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return self::$sum; |
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} |
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return self::$sum = new class implements AccumulatorInterface { |
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public function __invoke($carry, $item) { return $carry + $item; } |
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public function initial() { return 0; } |
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}; |
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} |
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/** |
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* Perform a multiplication on each elements of the stream |
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* |
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* <code> |
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* $stream = new ArrayStream([2, 5, 4]); |
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* $stream->reduce(Accumulators::multiply()); // 80 |
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* </code> |
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* |
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* @template V as numeric |
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* |
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* @return AccumulatorInterface<V, V> |
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*/ |
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public static function multiply() |
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{ |
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if (self::$multiply) { |
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2 |
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return self::$multiply; |
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} |
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return self::$multiply = new class implements AccumulatorInterface { |
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public function __invoke($carry, $item) { return $carry * $item; } |
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public function initial() { return 1; } |
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}; |
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} |
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/** |
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* Get the lowest element of the stream |
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* |
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* <code> |
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* $stream = new ArrayStream([8, 5, 4]); |
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* $stream->reduce(Accumulators::min()); // 4 |
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* </code> |
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* |
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* @template V |
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* |
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* @return AccumulatorInterface<V, V> |
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*/ |
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public static function min() |
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{ |
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if (self::$min) { |
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return self::$min; |
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} |
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return self::$min = new class implements AccumulatorInterface { |
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public function __invoke($carry, $item) { return $item < $carry ? $item : $carry; } |
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public function initial() { return PHP_INT_MAX; } |
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}; |
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} |
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/** |
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* Get the highest element of the stream |
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* |
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* <code> |
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* $stream = new ArrayStream([4, 8, 2]); |
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* $stream->reduce(Accumulators::max()); // 8 |
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* </code> |
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* |
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* @template V as numeric |
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* |
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* @return AccumulatorInterface<V, V> |
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*/ |
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2 |
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public static function max() |
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{ |
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2 |
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if (self::$max) { |
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return self::$max; |
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} |
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return self::$max = new class implements AccumulatorInterface { |
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public function __invoke($carry, $item) { return $item > $carry ? $item : $carry; } |
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public function initial() { return PHP_INT_MIN; } |
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}; |
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} |
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} |
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In the issue above, the returned value is violating the contract defined by the mentioned interface.
Let's take a look at an example: