From 74308fb8e1bf6036214e3c9409261b94384c2f01 Mon Sep 17 00:00:00 2001
From: Lexidor Digital <31805625+lexidor@users.noreply.github.com>
Date: Sat, 21 Feb 2026 11:56:11 +0000
Subject: [PATCH] Fix stack-like behavior in 46-generic-types.md

Seealso: https://github.com/hhvm/user-documentation/issues/1171
Seealso: https://github.com/hhvm/user-documentation/pull/1183
---
 manual/hack/10-types/46-generic-types.md | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/manual/hack/10-types/46-generic-types.md b/manual/hack/10-types/46-generic-types.md
index f1766163c..7f20fde3d 100644
--- a/manual/hack/10-types/46-generic-types.md
+++ b/manual/hack/10-types/46-generic-types.md
@@ -9,23 +9,24 @@ Consider the following example in which `Stack` is a generic class having one ty
 class StackUnderflowException extends Exception {}
 
 class Stack<T> {
-  private vec<T> $stack;
-  private int $stackPtr;
-
-  public function __construct() {
-    $this->stackPtr = 0;
-    $this->stack = vec[];
-  }
+  private vec<T> $stack = vec[];
+  private int $stackPtr = -1;
 
   public function push(T $value): void {
-    $this->stack[] = $value;
     $this->stackPtr++;
+    if (C\count($this->stack) === $this->stackPtr) {
+      $this->stack[] = $value;
+    } else {
+      $this->stack[$this->stackPtr] = $value;
+    }
   }
 
   public function pop(): T {
-    if ($this->stackPtr > 0) {
+    if ($this->stackPtr >= 0) {
+      $element = $this->stack[$this->stackPtr];
+      $this->stack[$this->stackPtr] = $this->stack[0];
       $this->stackPtr--;
-      return $this->stack[$this->stackPtr];
+      return $element;
     } else {
       throw new StackUnderflowException();
     }