Make Promise.is only check andThennable

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

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: 

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
 
 --[[