isBool

src/Type.php

@@ -46,4 +46,16 @@ public function asInt(): int
 
         return $this->variable;
     }
+
+    /**
+     * Asserts and narrow down the type to boolean.
+     */
+    public function isBool(): bool
+    {
+        if (! is_bool($this->variable)) {
+            throw new TypeError('Variable is not a boolean.');
+        }
+
+        return $this->variable;
+    }
 }

tests/IsBoolTest.php

@@ -0,0 +1,15 @@
+<?php
+
+test('boolean type', function () {
+    $variable = true;
+
+    $value = type($variable)->isBool();
+
+    expect($value)->toBeBool();
+});
+
+test('not boolean type', function () {
+    $variable = 7415541;
+
+    type($variable)->isBool();
+})->throws(TypeError::class, 'Variable is not a boolean.');