Online PHP editor | output for ncsGq

<?php declare(strict_types = 1); class Collection { private $_items; public function __construct(array $items = [])/*: void*/ { $this->_items = $items; } public function filter(callable $callback): self { foreach ($this->_items as $key => $value) if (!call_user_func($callback, $value)) unset($this->_items[$key]); return $this; } public function map(callable $callback): self { foreach ($this->_items as $key => $value) $this->_items[$key] = call_user_func($callback, $key, $value); return $this; } public function reindex(): self { $this->_items = array_values($this->_items); return $this; } public function sprintf(string $format): self { return $this->map(function ($key, $value) use ($format) { return substr_count($format, '%s') === 1 ? sprintf($format, $value) : sprintf($format, $key, $value); }); } public function keys(): self { $this->_items = array_keys($this->_items); return $this; } public function implode(string $delimiter = ''): string { $output = ''; $first = TRUE; foreach ($this->_items as $value) if ($first) { $output .= $value; $first = FALSE; } else $output .= "$delimiter$value"; return $output; } public static function index($index): callable { return function ($key, $value) use ($index) { return $value[$index]; }; } public static function property(string $property): callable { return function ($key, $value) use ($property) { return $value->$property; }; } public function values(): array { return $this->_items; } } class Filter { public static function not(callable $callback): callable { return function ($value) use ($callback) { return !call_user_func($callback, $value); }; } } echo (new Collection([ 42, 'one', 'two', ['foo' => 'BAR'], 'three', ['foo' => 'BAZ'], ])) ->filter(Filter::not('is_string')) ->filter('is_array') ->map(Collection::index('foo')) ->reindex() //->keys() //->sprintf('(%s,%s)') ->implode('_');