From f56140fe01678c4ca0c9803298e55bbcfde5f1db Mon Sep 17 00:00:00 2001
From: Lexidor Digital <31805625+lexidor@users.noreply.github.com>
Date: Tue, 21 Jan 2020 22:38:27 +0100
Subject: [PATCH] Backport Ref<T> to 4.0 (#114)

* Backport Ref<T> to 4.0

* Find the best hhvm that still passes travis

* Remove failing hhvm versions

Only hhvm 4.0 passes, since the others assume that `<?hh` means `// strict` instead of `// partial`
---
 .travis.yml |  3 ++-
 src/Ref.php | 28 ++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 src/Ref.php

diff --git a/.travis.yml b/.travis.yml
index b7ae2d31..b43ba207 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,7 +2,8 @@ sudo: required
 language: generic
 services: docker
 env:
- - HHVM_VERSION=latest
+ - HHVM_VERSION=4.0-latest
+ 
 install:
  - docker pull hhvm/hhvm:$HHVM_VERSION
 script:
diff --git a/src/Ref.php b/src/Ref.php
new file mode 100644
index 00000000..06368c4c
--- /dev/null
+++ b/src/Ref.php
@@ -0,0 +1,28 @@
+<?hh // strict
+/*
+ *  Copyright (c) 2004-present, Facebook, Inc.
+ *  All rights reserved.
+ *
+ *  This source code is licensed under the MIT license found in the
+ *  LICENSE file in the root directory of this source tree.
+ *
+ */
+
+namespace HH\Lib;
+
+/** Wrapper class for getting object (byref) semantics for a value type.
+ *
+ * This is especially useful for mutating values outside of a lambda's scope.
+ *
+ * In general, it's preferable to refactor to use return values or `inout`
+ * parameters instead of using this class - however, a `Ref` of a Hack array
+ * is generally preferable to a Hack collection - e.g. prefer `Ref<vec<T>>`
+ * over `Vector<T>`.
+ *
+ * `C\reduce()` and `C\reduce_with_key()` can also be used in some situations
+ * to avoid this class.
+ */
+final class Ref<T> {
+  <<__RxShallow>>
+  public function __construct(public T $value) {}
+}