added Structure::extend() [Closes #66]

src/Schema/Elements/Structure.php

@@ -76,6 +76,12 @@ public function skipDefaults(bool $state = true): self
 	}
 
 
+	public function extend(array $items): self
+	{
+		return new self($items + $this->items);
+	}
+
+
 	/********************* processing ****************d*g**/
 
 

tests/Schema/Expect.structure.phpt

@@ -501,3 +501,13 @@ test('processing without default values skipped on structure', function () {
 		$processor->process($schema, []),
 	);
 });
+
+
+test('extend', function () {
+	$schema = Expect::structure(['a' => Expect::string(), 'b' => Expect::string()]);
+
+	Assert::equal(
+		Expect::structure(['a' => Expect::int(), 'b' => Expect::string(), 'c' => Expect::int()]),
+		$schema->extend(['a' => Expect::int(), 'c' => Expect::int()]),
+	);
+});