added __with__ function according to proposed syntax in issue #29

2 files changed, 25 insertions, 4 deletions

diff --git a/lib/__set__.js b/lib/__set__.js
index 0fa88ac..ad0e5b0 100644
--- a/lib/__set__.js
+++ b/lib/__set__.js
@@ -46,4 +46,21 @@ function __set__() {
     };
 }
 
-module.exports = __set__;
+function __with__() {
+  var args = arguments;
+  return function(callback) {
+    if (typeof callback !== "function") {
+      throw new TypeError("__with__ expects a callback function")
+    }
+
+    var undo = __set__.apply(null, args)
+    try {
+      callback();
+    }
+    finally {
+      undo();
+    }
+  }
+}
+
+module.exports = {"__set__": __set__, "__with__": __with__}
diff --git a/lib/rewire.js b/lib/rewire.js
index 3daacef..61160fd 100644
--- a/lib/rewire.js
+++ b/lib/rewire.js
@@ -1,13 +1,16 @@
 var Module = require("module"),
     fs = require("fs"),
     __get__ = require("./__get__.js"),
-    __set__ = require("./__set__.js"),
+    setModule = require ("./__set__.js"),
+    __set__ = setModule["__set__"],
+    __with__ = setModule["__with__"],
     getImportGlobalsSrc = require("./getImportGlobalsSrc.js"),
     detectStrictMode = require("./detectStrictMode.js"),
     moduleEnv = require("./moduleEnv.js");
 
 var __get__Src = __get__.toString(),
-    __set__Src = __set__.toString();
+    __set__Src = __set__.toString(),
+    __with_Src = __with__.toString();
 
 /**
  * Does actual rewiring the module. For further documentation @see index.js
@@ -44,6 +47,7 @@ function internalRewire(parentModulePath, targetPath) {
     appendix = "\n";
     appendix += "module.exports.__set__ = " + __set__Src + "; ";
     appendix += "module.exports.__get__ = " + __get__Src + "; ";
+    appendix += "module.exports.__with__ = " + __with_Src + "; ";
 
     // Check if the module uses the strict mode.
     // If so we must ensure that "use strict"; stays at the beginning of the module.
@@ -58,4 +62,4 @@ function internalRewire(parentModulePath, targetPath) {
     return targetModule.exports;
 }
 
-module.exports = internalRewire;
\ No newline at end of file
+module.exports = internalRewire;