use singleton pattern for some amount of memory saving

Author: ianhoffman

src/Codegen/Constraints/UntypedBuilder.php

@@ -170,7 +170,7 @@ private function generateOneOfChecks(vec<TSchema> $schemas, HackBuilder $hb): vo
       ->addAssignment('$passed_any', false, HackBuilderValues::export())
       ->addAssignment('$passed_multi', false, HackBuilderValues::export())
       // Use `sentinal` rather than `null` so that it's obvious when we failed to match any constraint.
-      ->addAssignment('$output', Str\format('new \%s()', Sentinal::class), HackBuilderValues::literal())
+      ->addAssignment('$output', Str\format('\%s::get()', Sentinal::class), HackBuilderValues::literal())
       ->startForeachLoop('$constraints', null, '$constraint')
       ->startTryBlock()
       ->addMultilineCall('$output = $constraint', vec['$input', '$pointer'])

src/Sentinal.hack

@@ -3,4 +3,14 @@ namespace Slack\Hack\JsonSchema;
 /**
  * Represents an unset value.
  */
-final class Sentinal {}
+final class Sentinal {
+
+    /**
+     * The singleton instance of the sentinal value.
+     */
+    public static function get(): this {
+        return new self();
+    }
+
+    private function __construct () {}
+}

tests/examples/codegen/AddressSchemaValidator.php

@@ -5,7 +5,7 @@
  * To re-generate this file run `make test`
  *
  *
- * @generated SignedSource<<884da88463b70fac29468fab117c4e1b>>
+ * @generated SignedSource<<7c546e3edf3430be1044abfffdf398cd>>
  */
 namespace Slack\Hack\JsonSchema\Tests\Generated;
 use namespace Slack\Hack\JsonSchema;
@@ -425,7 +425,7 @@ public static function check(
 
     $passed_any = false;
     $passed_multi = false;
-    $output = new \Slack\Hack\JsonSchema\Sentinal();
+    $output = \Slack\Hack\JsonSchema\Sentinal::get();
     foreach ($constraints as $constraint) {
       try {
         $output = $constraint($input, $pointer);

tests/examples/codegen/UntypedSchemaValidator.php

@@ -5,7 +5,7 @@
  * To re-generate this file run `make test`
  *
  *
- * @generated SignedSource<<90a3ca75ea51b3a416f721e6eb1828de>>
+ * @generated SignedSource<<8553bd28dc52954a5c87a8c2cb2f3b01>>
  */
 namespace Slack\Hack\JsonSchema\Tests\Generated;
 use namespace Slack\Hack\JsonSchema;
@@ -1036,7 +1036,7 @@ public static function check(
 
     $passed_any = false;
     $passed_multi = false;
-    $output = new \Slack\Hack\JsonSchema\Sentinal();
+    $output = \Slack\Hack\JsonSchema\Sentinal::get();
     foreach ($constraints as $constraint) {
       try {
         $output = $constraint($input, $pointer);
@@ -1099,7 +1099,7 @@ public static function check(
 
     $passed_any = false;
     $passed_multi = false;
-    $output = new \Slack\Hack\JsonSchema\Sentinal();
+    $output = \Slack\Hack\JsonSchema\Sentinal::get();
     foreach ($constraints as $constraint) {
       try {
         $output = $constraint($input, $pointer);
@@ -1191,7 +1191,7 @@ public static function check(
 
     $passed_any = false;
     $passed_multi = false;
-    $output = new \Slack\Hack\JsonSchema\Sentinal();
+    $output = \Slack\Hack\JsonSchema\Sentinal::get();
     foreach ($constraints as $constraint) {
       try {
         $output = $constraint($input, $pointer);