Add abstract references base #205

doc/caveats.md

@@ -6,9 +6,11 @@ satisfy **all** 6to5 feature requirements by using the included
 
 | Feature                     | Requirements                                                                                                                        |
 | --------------------------- | ----------------------------------------------------------------------------------------------------------------------------------- |
+| Abstract References         | `Symbol`                                                                                                                            |
 | Array destructuring         | `Array.isArray`, `Array.from`                                                                                                       |
 | Async functions, Generators | [experimental option](usage.md#experimental), [regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) |
 | Comprehensions              | [experimental option](usage.md#experimental), `Array.isArray`, `Array.from`                                                         |
+| For..Of                     | `Symbol`, `prototype[Symbol.iterator]`                                                                                              |
 | Spread                      | `Array.isArray`, `Array.from`                                                                                                       |
 
 ## Classes
@@ -36,14 +38,3 @@ class Bar extends Foo {
   }
 }
 ```
-
-## Constructor spread
-
-Constructor spreads do not currently support built-ins. ie.
-`new Array(...items)`.
-
-## For-of
-
-A polyfill is required for for-of functionality that implements `Symbol` and
-adds `prototype[Symbol.iterator]` behaviour to built-ins. Using the polyfills
-specified in [polyfill](polyfill.md) suffices.

doc/differences.md

@@ -69,6 +69,7 @@ better suited if you'd like a full ES6 environment with polyfills and all.
 
 |                              | 6to5  | Traceur | es6-transpiler | esnext | es6now | jstransform |
 | ---------------------------- | ----- | ------- | -------------- | ------ | ------ | ----------- |
+| Abstract references          | ✓     |         |                |        |        |             |
 | Array comprehension          | ✓     | ✓       | ✓              |        |        |             |
 | Arrow functions              | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
 | Async functions              | ✓     | ✓       |                | ✓      |        |             |

doc/features.md

@@ -1,5 +1,13 @@
 # Features
 
+## Abstract references ([experimental](usage.md#experimental))
+
+```javascript
+foo::bar;
+foo::bar = baz;
+delete foo::bar;
+```
+
 ## Array comprehension ([experimental](usage.md#experimental))
 
 ```javascript

doc/index.md

@@ -31,6 +31,7 @@ And it doesn't end here! To see all the ways you can use 6to5, check out the
 
 ## [Features](features.md)
 
+ - [Abstract references](features.md#abstract-references) ([experimental](usage.md#experimental))
  - [Array comprehension](features.md#array-comprehension) ([experimental](usage.md#experimental))
  - [Async functions](features.md#async-functions) ([experimental](usage.md#experimental))
  - [Arrow functions](features.md#arrow-functions)

lib/6to5/polyfill.js

@@ -1,6 +1,35 @@
+//
+
+var ensureSymbol = function (key) {
+  Symbol[key] = Symbol[key] || Symbol();
+};
+
+var ensureProto = function (Constructor, key, val) {
+  var proto = Constructor.prototype;
+  proto[key] = proto[key] || val;
+};
+
+//
+
 if (typeof Symbol === "undefined") {
   require("es6-symbol/implement");
 }
 
 require("es6-shim");
 require("./transformation/transformers/generators/runtime");
+
+// Abstract references
+
+ensureSymbol("referenceGet");
+ensureSymbol("referenceSet");
+ensureSymbol("referenceDelete");
+
+ensureProto(Function, Symbol.referenceGet, function () { return this });
+
+ensureProto(Map, Symbol.referenceGet, Map.prototype.get);
+ensureProto(Map, Symbol.referenceSet, Map.prototype.set);
+ensureProto(Map, Symbol.referenceDelete, Map.prototype.delete);
+
+ensureProto(WeakMap, Symbol.referenceGet, WeakMap.prototype.get);
+ensureProto(WeakMap, Symbol.referenceSet, WeakMap.prototype.set);
+ensureProto(WeakMap, Symbol.referenceDelete, WeakMap.prototype.delete);

lib/6to5/transformation/transform.js

@@ -47,6 +47,7 @@ _.each({
   forOf:                     require("./transformers/for-of"),
   unicodeRegex:              require("./transformers/unicode-regex"),
   react:                     require("./transformers/react"),
+  abstractReferences:        require("./transformers/abstract-references"),
 
   constants:                 require("./transformers/constants"),
   letScoping:                require("./transformers/let-scoping"),

test/fixtures/transformation/abstract-references/delete/actual.js

@@ -0,0 +1 @@
+delete foo::bar;

test/fixtures/transformation/abstract-references/delete/expected.js

@@ -0,0 +1,3 @@
+"use strict";
+
+bar[Symbol.referenceDelete](foo);

test/fixtures/transformation/abstract-references/get/actual.js

@@ -0,0 +1 @@
+foo::bar;

test/fixtures/transformation/abstract-references/get/expected.js

@@ -0,0 +1,3 @@
+"use strict";
+
+bar[Symbol.referenceGet](foo);

test/fixtures/transformation/abstract-references/set/actual.js

@@ -0,0 +1 @@
+foo::bar = baz;

test/fixtures/transformation/abstract-references/set/expected.js

@@ -0,0 +1,3 @@
+"use strict";
+
+bar[Symbol.referenceSet](foo, baz);