`get_deep_value`, a version of `_.get` for PHP

get-deep-value-Test.php

<?php

require_once( 'get-deep-value.php' );

/**
 * @runTestsInSeparateProcess
 */
class Get_Deep_Value_Test extends PHPUnit_Framework_TestCase {

	use Codeception\Specify;

	public function test_get_deep_value() {
		$this->specify( 'returns null if the haystack is empty', function() {
			$haystack = [];
			$key_path = [ 'one', 'two' ];
			$actual = Get_Deep_Value::get_deep_value( $haystack, $key_path );
			$expected = null;
			expect( $actual )->equals( $expected );
		} );

		$this->specify( 'returns null if the haystack does not contain the first key', function() {
			$haystack = [ 'three' => 'foo' ];
			$key_path = [ 'one', 'two' ];
			$actual = Get_Deep_Value::get_deep_value( $haystack, $key_path );
			$expected = null;
			expect( $actual )->equals( $expected );
		} );

		$this->specify( 'returns null if the haystack does not contain the second key', function() {
			$haystack = [ 'one' => [ 'three' => 'foo' ] ];
			$key_path = [ 'one', 'two' ];
			$actual = Get_Deep_Value::get_deep_value( $haystack, $key_path );
			$expected = null;
			expect( $actual )->equals( $expected );
		} );

		$this->specify( 'returns the second value if the haystack does contain the second key', function() {
			$haystack = [ 'one' => [ 'two' => 'foo' ] ];
			$key_path = [ 'one', 'two' ];
			$actual = Get_Deep_Value::get_deep_value( $haystack, $key_path );
			$expected = 'foo';
			expect( $actual )->equals( $expected );
		} );

		$this->specify( 'returns the third value if the haystack does contain the third key', function() {
			$haystack = [ 'one' => [ 'two' => [ 'four' => 'bar', 'three' => 'foo' ] ] ];
			$key_path = [ 'one', 'two', 'three' ];
			$actual = Get_Deep_Value::get_deep_value( $haystack, $key_path );
			$expected = 'foo';
			expect( $actual )->equals( $expected );
		} );
	}
}

get-deep-value.php

<?php

class Get_Deep_Value {
	/**
	 * Return a deeply nested value of an array if it exists
	 *
	 * @param array $haystack The associative array to search
	 * @param array $key_path An ordered set of keys in the $haystack
	 *
	 * @return mixed|null The value last element of the nested array  in the key path
	 */
	public static function get_deep_value( $haystack, $key_path ) {
		$key = array_shift( $key_path );
		if ( ! isset( $haystack[ $key ] ) ) {
			return null;
		}
		if ( empty( $key_path ) ) {
			return $haystack[ $key ];
		}
		return self::get_deep_value( $haystack[ $key ], $key_path );
	}
}