ES6 symbols: turn symbols into a proper primitive type

src/symbol.js

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 "use strict";
 
-var $Symbol = function() { return %CreateSymbol() }
-global.Symbol = $Symbol
+var $Symbol = global.Symbol;
 
-// Symbols only have a toString method and no prototype.
-var SymbolDelegate = {
-  __proto__: null,
-  toString: $Object.prototype.toString
+function SymbolConstructor(x) {
+  var value = IS_SYMBOL(x) ? x : %CreateSymbol();
+  if (%_IsConstructCall()) {
+    %_SetValueOf(this, value);
+  } else {
+    return value;
+  }
 }
 
-$Object.freeze(SymbolDelegate)
+function SymbolToString() {
+  throw new $TypeError("Symbol.prototype.toString is not allowed");

[Michael Starzinger, 2013/03/22 11:39:04]

See comments below about MakeTypeError, maybe you can find a message that suits
this error or you might have to add a new one.

[rossberg, 2013/03/22 12:37:44]

Done.

+}
+
+function SymbolValueOf() {
+  // NOTE: Both Symbol objects and values can enter here as
+  // 'this'. This is not as dictated by ECMA-262.
+  if (!IS_SYMBOL(this) && !IS_SYMBOL_WRAPPER(this)) {
+    throw new $TypeError("Symbol.prototype.valueOf is not generic");

[Michael Starzinger, 2013/03/22 11:39:04]

Use the following to generate the TypeError instead. This allows us to have one
single choke-point where all error objects and messages are generated.

throw MakeTypeError('incompatible_method_receiver',
                    ['Symbol.prototype.valueOf', this]);

[rossberg, 2013/03/22 12:37:44]

Done.

+  }
+  return %_ValueOf(this);
+}
+
+//-------------------------------------------------------------------
+
+function SetUpSymbol() {
+  %CheckIsBootstrapping();
+
+  %SetCode($Symbol, SymbolConstructor);
+  %FunctionSetPrototype($Symbol, new $Symbol());
+  %SetProperty($Symbol.prototype, "constructor", $Symbol, DONT_ENUM);
+
+  InstallFunctions($Symbol.prototype, DONT_ENUM, $Array(
+    "toString", SymbolToString,
+    "valueOf", SymbolValueOf
+  ));
+}
+
+SetUpSymbol();