From 1a0ec7db47721a0fc82ae64456100457448148a3 Mon Sep 17 00:00:00 2001
From: Eryn Lynn <eryn@eryn.io>
Date: Sun, 22 Sep 2019 22:58:23 -0400
Subject: [PATCH] Make Promise.is only check andThennable

---
 CHANGELOG.md  | 4 ++++
 lib/README.md | 2 +-
 lib/init.lua  | 7 +------
 3 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index af967f0..05e6bdd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 2.4.0
+
+- `Promise.is` now only checks if the object is "andThennable" (has an `andThen` method).
+
 # 2.3.1
 
 - Make unhandled rejection warning trigger on next Heartbeat
diff --git a/lib/README.md b/lib/README.md
index 892bf42..3a89d8c 100644
--- a/lib/README.md
+++ b/lib/README.md
@@ -186,7 +186,7 @@ docs:
       params: "promises: array<Promise<T>>"
       returns: Promise<T>
     - name: is
-      desc: Returns whether the given object is a Promise.
+      desc: Returns whether the given object is a Promise. This only checks if the object is a table and has an `andThen` method.
       static: true
       params: "object: any"
       returns: 
diff --git a/lib/init.lua b/lib/init.lua
index 492d625..88f2bd9 100644
--- a/lib/init.lua
+++ b/lib/init.lua
@@ -67,8 +67,6 @@ local function createSymbol(name)
 	return symbol
 end
 
-local PromiseMarker = createSymbol("PromiseMarker")
-
 local Promise = {}
 Promise.prototype = {}
 Promise.__index = Promise.prototype
@@ -101,9 +99,6 @@ function Promise.new(callback, parent)
 		-- Used to locate where a promise was created
 		_source = debug.traceback(),
 
-		-- A tag to identify us as a promise
-		[PromiseMarker] = true,
-
 		_status = Promise.Status.Started,
 
 		-- A table containing a list of all results, whether success or failure.
@@ -300,7 +295,7 @@ function Promise.is(object)
 		return false
 	end
 
-	return object[PromiseMarker] == true
+	return type(object.andThen) == "function"
 end
 
 --[[