Add when and unless for conditional value resolution

composer.json

@@ -122,7 +122,9 @@
             "src/Functional/True.php",
             "src/Functional/Truthy.php",
             "src/Functional/Unique.php",
+            "src/Functional/Unless.php",
             "src/Functional/ValueToKey.php",
+            "src/Functional/When.php",
             "src/Functional/With.php",
             "src/Functional/Zip.php",
             "src/Functional/ZipAll.php"

docs/functional-php.md

@@ -1036,6 +1036,35 @@ use function Functional\tap;
 tap(create_user('John Doe'), fn ($user) => send_welcome_email($user))->login();
 ```
 
+## when()
+
+``mixed when(mixed|Closure $condition, mixed|Closure $value, mixed|Closure $default = null)``
+Return a value if the given condition is true. All three arguments can be closures — `$condition` is evaluated, and `$value` or `$default` is resolved accordingly.
+
+```php
+use function Functional\when;
+
+when(true, 'yes');              // 'yes'
+when(false, 'yes');             // null
+when(false, 'yes', 'no');      // 'no'
+when(fn () => true, 'yes');    // 'yes'
+when(true, fn () => 'computed'); // 'computed'
+```
+
+## unless()
+
+``mixed unless(mixed|Closure $condition, mixed|Closure $value, mixed|Closure $default = null)``
+Return a value if the given condition is false. The inverse of `when()`.
+
+```php
+use function Functional\unless;
+
+unless(false, 'yes');           // 'yes'
+unless(true, 'yes');            // null
+unless(true, 'yes', 'no');     // 'no'
+unless(fn () => false, 'yes'); // 'yes'
+```
+
 ## repeat()
 
 Creates and returns a function that can be used to execute the given closure multiple times.

src/Functional/Functional.php

@@ -493,11 +493,21 @@ final class Functional
      */
     const unique = '\Functional\unique';
 
+    /**
+     * @see \Functional\unless
+     */
+    const unless = '\Functional\unless';
+
     /**
      * @see \Functional\value_to_key
      */
     const value_to_key = '\Functional\value_to_key';
 
+    /**
+     * @see \Functional\when
+     */
+    const when = '\Functional\when';
+
     /**
      * @see \Functional\with
      */

src/Functional/Unless.php

@@ -0,0 +1,32 @@
+<?php
+
+/**
+ * @package   Functional-php
+ * @author    Lars Strojny <lstrojny@php.net>
+ * @copyright 2011-2021 Lars Strojny
+ * @license   https://opensource.org/licenses/MIT MIT
+ * @link      https://github.com/lstrojny/functional-php
+ */
+
+namespace Functional;
+
+/**
+ * Return a value if the given condition is false.
+ *
+ * @param mixed|\Closure $condition
+ * @param mixed|\Closure $value
+ * @param mixed|\Closure $default
+ *
+ * @return mixed
+ * @no-named-arguments
+ */
+function unless($condition, $value, $default = null)
+{
+    $condition = $condition instanceof \Closure ? $condition() : $condition;
+
+    if (!$condition) {
+        return $value instanceof \Closure ? $value($condition) : $value;
+    }
+
+    return $default instanceof \Closure ? $default($condition) : $default;
+}

src/Functional/When.php

@@ -0,0 +1,32 @@
+<?php
+
+/**
+ * @package   Functional-php
+ * @author    Lars Strojny <lstrojny@php.net>
+ * @copyright 2011-2021 Lars Strojny
+ * @license   https://opensource.org/licenses/MIT MIT
+ * @link      https://github.com/lstrojny/functional-php
+ */
+
+namespace Functional;
+
+/**
+ * Return a value if the given condition is true.
+ *
+ * @param mixed|\Closure $condition
+ * @param mixed|\Closure $value
+ * @param mixed|\Closure $default
+ *
+ * @return mixed
+ * @no-named-arguments
+ */
+function when($condition, $value, $default = null)
+{
+    $condition = $condition instanceof \Closure ? $condition() : $condition;
+
+    if ($condition) {
+        return $value instanceof \Closure ? $value($condition) : $value;
+    }
+
+    return $default instanceof \Closure ? $default($condition) : $default;
+}

tests/Functional/UnlessTest.php

@@ -0,0 +1,59 @@
+<?php
+
+/**
+ * @package   Functional-php
+ * @author    Lars Strojny <lstrojny@php.net>
+ * @copyright 2011-2021 Lars Strojny
+ * @license   https://opensource.org/licenses/MIT MIT
+ * @link      https://github.com/lstrojny/functional-php
+ */
+
+namespace Functional\Tests;
+
+use function Functional\unless;
+
+class UnlessTest extends AbstractTestCase
+{
+    public function testUnlessConditionIsFalsy(): void
+    {
+        self::assertEquals('yes', unless(false, 'yes'));
+    }
+
+    public function testUnlessConditionIsTruthy(): void
+    {
+        self::assertNull(unless(true, 'yes'));
+    }
+
+    public function testUnlessConditionIsTruthyWithDefault(): void
+    {
+        self::assertEquals('no', unless(true, 'yes', 'no'));
+    }
+
+    public function testUnlessValueIsClosure(): void
+    {
+        self::assertEquals('fallback', unless(false, function () {
+            return 'fallback';
+        }));
+    }
+
+    public function testUnlessDefaultIsClosure(): void
+    {
+        self::assertEquals('default', unless(true, 'yes', function () {
+            return 'default';
+        }));
+    }
+
+    public function testUnlessConditionIsClosure(): void
+    {
+        self::assertEquals('yes', unless(function () {
+            return false;
+        }, 'yes'));
+    }
+
+    public function testUnlessConditionIsClosureReturningTruthy(): void
+    {
+        self::assertNull(unless(function () {
+            return true;
+        }, 'yes'));
+    }
+}

tests/Functional/WhenTest.php

@@ -0,0 +1,59 @@
+<?php
+
+/**
+ * @package   Functional-php
+ * @author    Lars Strojny <lstrojny@php.net>
+ * @copyright 2011-2021 Lars Strojny
+ * @license   https://opensource.org/licenses/MIT MIT
+ * @link      https://github.com/lstrojny/functional-php
+ */
+
+namespace Functional\Tests;
+
+use function Functional\when;
+
+class WhenTest extends AbstractTestCase
+{
+    public function testWhenConditionIsTruthy(): void
+    {
+        self::assertEquals('yes', when(true, 'yes'));
+    }
+
+    public function testWhenConditionIsFalsy(): void
+    {
+        self::assertNull(when(false, 'yes'));
+    }
+
+    public function testWhenConditionIsFalsyWithDefault(): void
+    {
+        self::assertEquals('no', when(false, 'yes', 'no'));
+    }
+
+    public function testWhenValueIsClosure(): void
+    {
+        self::assertEquals('condition was true', when(true, function ($condition) {
+            return $condition ? 'condition was true' : 'condition was false';
+        }));
+    }
+
+    public function testWhenDefaultIsClosure(): void
+    {
+        self::assertEquals('fallback', when(false, 'yes', function () {
+            return 'fallback';
+        }));
+    }
+
+    public function testWhenConditionIsClosure(): void
+    {
+        self::assertEquals('yes', when(function () {
+            return true;
+        }, 'yes'));
+    }
+
+    public function testWhenConditionIsClosureReturningFalsy(): void
+    {
+        self::assertNull(when(function () {
+            return false;
+        }, 'yes'));
+    }
+}