add Is::just()

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 - `Shape::rename()` to rename a key in the output array
 - `Shape::default()` to specify a default value when an optional key is not set
+- `Is::just()`
 
 ## 1.5.0 - 2024-11-10
 

docs/constraints/maybe.md

@@ -0,0 +1,15 @@
+# Maybe monad
+
+If a previous contraint outputs a [`Maybe`](https://innmind.org/Immutable/structures/maybe/) and you want to access the inner value you can do:
+
+```php
+use Innmind\Validation\Is;
+use Innmind\Immutable\Maybe;
+
+$validate = Is::int()
+    ->or(Is::null())
+    ->map(Maybe::of(...))
+    ->and(Is::just());
+```
+
+In this example the input can be an `int` or `null` but it will fail the validation in case the value is `null` because `Maybe::of(...)` will move the `null` as a `Nothing` and we say we want a `Just`.

mkdocs.yml

@@ -11,6 +11,7 @@ nav:
     - Array shapes: constraints/array-shapes.md
     - Dates: constraints/dates.md
     - Objects: constraints/objects.md
+    - Maybe monad: constraints/maybe.md
     - Custom: constraints/custom.md
 
 theme:

proofs/is.php

@@ -2,7 +2,10 @@
 declare(strict_types = 1);
 
 use Innmind\Validation\Is;
-use Innmind\Immutable\Str;
+use Innmind\Immutable\{
+    Str,
+    Maybe,
+};
 use Innmind\BlackBox\Set;
 
 return static function() {
@@ -615,4 +618,29 @@ static function($assert, $keys, $values, $integer, $string, $random) {
             );
         },
     );
+
+    yield proof(
+        'Is::just()',
+        given(Set\Integers::any()),
+        static function($assert, $value) {
+            $assert->same(
+                $value,
+                Is::int()
+                    ->map(Maybe::just(...))
+                    ->and(Is::just())($value)->match(
+                        static fn($value) => $value,
+                        static fn() => null,
+                    ),
+            );
+
+            $assert->false(
+                Is::null()
+                    ->map(Maybe::of(...))
+                    ->and(Is::just())(null)->match(
+                        static fn($value) => $value,
+                        static fn() => false,
+                    ),
+            );
+        },
+    );
 };

src/Is.php

@@ -5,6 +5,7 @@
 
 use Innmind\Immutable\{
     Validation,
+    Maybe,
     Predicate as PredicateInterface,
 };
 
@@ -162,6 +163,25 @@ public static function associativeArray(Constraint $key, Constraint $value): Ass
         return AssociativeArray::of($key, $value);
     }
 
+    /**
+     * @psalm-pure
+     * @template V
+     *
+     * @param ?non-empty-string $message
+     *
+     * @return Constraint<Maybe<V>, V>
+     */
+    public static function just(?string $message = null): Constraint
+    {
+        /** @psalm-suppress MixedArgumentTypeCoercion */
+        return Of::callable(static fn(Maybe $value) => $value->match(
+            Validation::success(...),
+            static fn() => Validation::fail(Failure::of(
+                $message ?? 'No value was provided',
+            )),
+        ));
+    }
+
     /**
      * @param non-empty-string $message
      *