Merge pull request #9 from christav/setFunc

Added setFunc - give a function to retrieve a value instead of the value

README.md

@@ -5,8 +5,7 @@ This module makes it easy to use express-style configuration for any application
 It allows your users to define separate configuration environments in code
 and switch between sets of configuration via a single environment variable.
 
-
-Usage:
+## Basic Usage
 
 ```javascript
 
@@ -50,8 +49,28 @@ process.env.MY_LIBRARY_VAR = 'production';
 c.default.get('settingTwo').should.equal('prodValue');
 ```
 
-Do you want to add helper methods for your specific configuration? It's easy
-with a config customizer:
+## Setting Getters
+
+Instead of a setting a simple value, you can instead use the setFunc method to
+provide a function that will run when the value is requested:
+
+```javascript
+var c2 = envconf.createConfig();
+
+c2.configure('development', function (c) {
+  c.setFunc('settingOne', function () { return 'This value came from a function'; });
+});
+
+c2.get('settingOne').should.equal('This value came from a function');
+```
+
+This can be handy if you want to have a default value that you need to derive from
+ambient state.
+
+## Customizing the config object
+
+Do you want to add helper methods for your specific configuration? Or set specific
+values in every configuration? It's easy with a config customizer:
 
 ```javascript
 
@@ -73,6 +92,8 @@ c3.configure('production', function (c) {
 });
 ```
 
+## Saving and Restoring config values
+
 Are you making changes to a global configuration in your unit tests, and want
 to ensure you've restored the state after your test? Use a snapshot:
 
@@ -98,6 +119,8 @@ c4.get('originalValue').should.equal('one');
 
 Snapshot/restore also saves and restores any child configurations.
 
+## Temporary Configs
+
 Similarly, you might want to set up a configuration and then be able
 to throw it away without giving it a name. Easy:
 

lib/index.js

@@ -56,7 +56,12 @@ function Config(parent, defaultEnvVar, customizer) {
   };
 
   config.set = function (setting, value) {
-    settings[setting] = value;
+    settings[setting] = function () { return value; };
+    return this;
+  };
+
+  config.setFunc = function (setting, getter) {
+    settings[setting] = getter;
     return this;
   };
 
@@ -67,7 +72,7 @@ function Config(parent, defaultEnvVar, customizer) {
       }
       return undefined;
     }
-    return settings[setting];
+    return settings[setting]();
   };
 
   config.has = function (setting) {

test/config-test.js

@@ -372,3 +372,27 @@ describe('Temporary environments', function () {
     customizer.callCount.should.equal(2);
   });
 });
+
+describe('Setting getters', function () {
+  var c;
+
+  beforeEach(function () {
+    c = envconf.createConfig();
+  });
+
+  it('should call getter when retrieving', function () {
+    function getter() { return 'a value'; }
+    var spy = sinon.spy(getter);
+    c.setFunc('setting', spy);
+    c.get('setting').should.equal('a value');
+    spy.callCount.should.equal(1);
+  });
+
+  it('should not be invoked when set using set method', function () {
+    function getter() { return 'a value'; }
+    var spy = sinon.spy(getter);
+    c.set('setting', spy);
+    c.get('setting').should.equal(spy);
+    spy.callCount.should.equal(0);    
+  });
+});