Add a lift method to Option

Lifting allows to use any already existing function with Options as parameters. If any of the parameter is empty, we consider that we cannot call the original function and return None.

Closes #30.

Co-Authored-By: Gilles Crettenand <[email protected]>

src/PhpOption/Option.php

@@ -130,6 +130,43 @@ public static function ensure($value, $noneValue = null)
  }
  }
 
+ /**
+ * Lift a function so that it accepts Option as parameters.
+ *
+ * We return a new closure that wraps the original callback. If any of the
+ * parameters passed to the lifted function is empty, the function will
+ * return a value of None. Otherwise, we will pass all parameters to the
+ * original callback and return the value inside a new Option, unless an
+ * Option is returned from the function, in which case, we use that.
+ *
+ * @param callable $callback
+ * @param mixed $noneValue
+ *
+ * @return callable
+ */
+ public static function lift($callback, $noneValue = null)
+ {
+ return function() use ($callback, $noneValue)
+ {
+ $args = func_get_args();
+
+ // if at least one parameter is empty, return None
+ if (array_reduce($args, function ($status, Option $o) {
+ return $o->isEmpty() ? true : $status;
+ }, false)) {
+ return None::create();
+ }
+
+ $args = array_map(function (Option $o) {
+ // it is safe to do so because the fold above checked
+ // that all arguments are of type Some
+ return $o->get();
+ }, $args);
+
+ return self::ensure(call_user_func_array($callback, $args), $noneValue);
+ };
+ }
+
  /**
  * Returns the value if available, or throws an exception otherwise.
  *

tests/PhpOption/Tests/OptionTest.php

@@ -91,4 +91,35 @@ public function testOrElseWithMultipleAlternatives()
 
  $this->assertEquals('foo', $a->orElse($returns)->orElse($throws)->get());
  }
+
+ public function testLift()
+ {
+ $f = function ($a, $b) {
+ return $a + $b;
+ };
+
+ $fL = Option::lift($f);
+
+ $a = new Some(1);
+ $b = new Some(5);
+ $n = None::create();
+
+ $this->assertEquals(6, $fL($a, $b)->get());
+ $this->assertEquals(6, $fL($b, $a)->get());
+ $this->assertEquals($n, $fL($a, $n));
+ $this->assertEquals($n, $fL($n, $a));
+ $this->assertEquals($n, $fL($n, $n));
+ }
+
+ public function testLiftDegenerate()
+ {
+ $f = function () {
+ };
+
+ $fL1 = Option::lift($f);
+ $fL2 = Option::lift($f, false);
+
+ $this->assertEquals(None::create(), $fL1());
+ $this->assertEquals(Some::create(null), $fL2());
+ }
 }