Array/TypedArray/ArrayBuffer method subclassing and @@species

src/js/runtime.js

Index: src/js/runtime.js
diff --git a/src/js/runtime.js b/src/js/runtime.js
index af5f2da84cdccd4b2176fe609aca30711feddd7f..3ada50c49b1ac63e131fce62cdc0c3db47445c70 100644
--- a/src/js/runtime.js
+++ b/src/js/runtime.js
@@ -16,15 +16,22 @@
 
 %CheckIsBootstrapping();
 
+var FLAG_harmony_species;
 var GlobalArray = global.Array;
 var GlobalBoolean = global.Boolean;
 var GlobalString = global.String;
-var isConcatSpreadableSymbol =
-    utils.ImportNow("is_concat_spreadable_symbol");
 var MakeRangeError;
+var MakeTypeError;
+var speciesSymbol;
 
 utils.Import(function(from) {
   MakeRangeError = from.MakeRangeError;
+  MakeTypeError = from.MakeTypeError;
+  speciesSymbol = from.species_symbol;
+});
+
+utils.ImportFromExperimental(function(from) {
+  FLAG_harmony_species = from.FLAG_harmony_species;
 });
 
 // ----------------------------------------------------------------------------
@@ -118,6 +125,30 @@ function MinSimple(a, b) {
 %SetForceInlineFlag(MaxSimple);
 %SetForceInlineFlag(MinSimple);
 
+
+// ES2015 7.3.20
+function SpeciesConstructor(object, defaultConstructor) {
+  if (FLAG_harmony_species) {
+    var constructor = object.constructor;
+    if (IS_UNDEFINED(constructor)) {
+      return defaultConstructor;
+    }
+    if (!IS_RECEIVER(constructor)) {
+      throw MakeTypeError(kSpeciesNotConstructor);
+    }
+    var species = constructor[speciesSymbol];
+    if (IS_NULL_OR_UNDEFINED(species)) {
+      return defaultConstructor;
+    }
+    if (%IsConstructor(species)) {
+      return species;
+    }
+    throw MakeTypeError(kSpeciesNotConstructor);
+  } else {
+    return defaultConstructor;
+  }
+}
+
 //----------------------------------------------------------------------------
 
 // NOTE: Setting the prototype for Array must take place as early as
@@ -137,6 +168,7 @@ utils.Export(function(to) {
   to.SameValue = SameValue;
   to.SameValueZero = SameValueZero;
   to.ToPositiveInteger = ToPositiveInteger;
+  to.SpeciesConstructor = SpeciesConstructor;
 });
 
 %InstallToContext([