diff --git a/build/scscript-classlib.js b/build/scscript-classlib.js
index ce22e18..f285a62 100644
--- a/build/scscript-classlib.js
+++ b/build/scscript-classlib.js
@@ -231,9 +231,18 @@ SCScript.install(function(sc) {
     // TODO: implements equals
     // TODO: implements compareObject
     // TODO: implements instVarHash
-    // TODO: implements basicHash
-    // TODO: implements hash
-    // TODO: implements identityHash
+
+    spec.basicHash = function() {
+      return $SC.Integer(this._hash);
+    };
+
+    spec.hash = function() {
+      return $SC.Integer(this._hash);
+    };
+
+    spec.identityHash = function() {
+      return $SC.Integer(this._hash);
+    };
 
     spec["->"] = function($obj) {
       return $SC("Association").new(this, $obj);
@@ -1577,10 +1586,6 @@ SCScript.install(function(sc) {
       return $SC.Boolean(this.valueOf() !== $aMagnitude.valueOf());
     };
 
-    spec.hash = function() {
-      return this._subclassResponsibility("hash");
-    };
-
     spec["<"] = function($aMagnitude) {
       return $SC.Boolean(this < $aMagnitude);
     };
@@ -2145,8 +2150,6 @@ SCScript.install(function(sc) {
       return this.absdif($that) ["<"] ($precision);
     }, "that; precision=0.0001");
 
-    // TODO: implements hash
-
     spec.asInteger = function() {
       return $SC.Integer(this._);
     };
@@ -2535,7 +2538,9 @@ SCScript.install(function(sc) {
 
     spec.isInteger = utils.alwaysReturn$true;
 
-    // TODO: implements hash
+    spec.hash = function() {
+      return $SC.Float(this._).hash();
+    };
 
     [
       [ "+", $SC.Integer, $SC.Float ],
@@ -8055,7 +8060,9 @@ SCScript.install(function(sc) {
       return $false;
     };
 
-    // TODO: implements hash
+    spec.hash = function() {
+      return this._key.hash();
+    };
 
     spec["<"] = function($anAssociation) {
       return this._key ["<"] ($anAssociation.key());
diff --git a/build/scscript.js b/build/scscript.js
index 6adfbbd..e9ca31b 100644
--- a/build/scscript.js
+++ b/build/scscript.js
@@ -1,7 +1,7 @@
 (function(global) {
 "use strict";
 
-var sc = { VERSION: "0.0.32" };
+var sc = { VERSION: "0.0.33" };
 
 // src/sc/sc.js
 (function(sc) {
@@ -639,6 +639,7 @@ var sc = { VERSION: "0.0.32" };
   var klass       = {};
   var metaClasses = {};
   var classes     = klass.classes = {};
+  var hash = 0x100000;
 
   var createClassInstance = function(MetaSpec) {
     var instance = new SCClass();
@@ -675,7 +676,9 @@ var sc = { VERSION: "0.0.32" };
             className + bond + methodName + " is already defined."
         );
       }
-      methods[methodName] = func;
+      Object.defineProperty(methods, methodName, {
+        value: func, writable: true
+      });
     };
 
     if (typeof fn === "function") {
@@ -742,9 +745,11 @@ var sc = { VERSION: "0.0.32" };
     newClass = new MetaClass._MetaSpec();
     newClass._name = className;
     newClass._Spec = constructor;
-    constructor.prototype.__class = newClass;
-    constructor.prototype.__Spec  = constructor;
-    constructor.prototype.__className = className;
+    Object.defineProperties(constructor.prototype, {
+      __class: { value: newClass, writable: true },
+      __Spec : { value: constructor },
+      __className: { value: className }
+    });
     classes[className] = newClass;
 
     return newClass;
@@ -825,6 +830,9 @@ var sc = { VERSION: "0.0.32" };
     Object.defineProperties(this, {
       _immutable: {
         value: false, writable: true
+      },
+      _hash: {
+        value: hash++
       }
     });
   }
diff --git a/package.json b/package.json
index f2c160f..8e01e56 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "scscript",
-  "version": "0.0.32",
+  "version": "0.0.33",
   "author": "Nao Yonamine <mohayonao@gmail.com>",
   "homepage": "http://mohayonao.github.io/SCScript/",
   "bugs": "https://github.com/mohayonao/SCScript/issues",
diff --git a/src/sc/classlib/Collections/Association.js b/src/sc/classlib/Collections/Association.js
index 1e0feff..dc43637 100644
--- a/src/sc/classlib/Collections/Association.js
+++ b/src/sc/classlib/Collections/Association.js
@@ -44,7 +44,9 @@ SCScript.install(function(sc) {
       return $false;
     };
 
-    // TODO: implements hash
+    spec.hash = function() {
+      return this._key.hash();
+    };
 
     spec["<"] = function($anAssociation) {
       return this._key ["<"] ($anAssociation.key());
diff --git a/src/sc/classlib/Collections/Association_test.js b/src/sc/classlib/Collections/Association_test.js
index 124a648..88d876c 100644
--- a/src/sc/classlib/Collections/Association_test.js
+++ b/src/sc/classlib/Collections/Association_test.js
@@ -67,7 +67,13 @@
       test = instance ["=="] ($anAssociation);
       expect(test).to.be.a("SCBoolean").that.is.true;
     });
-    it.skip("#hash", function() {
+    it("#hash", function() {
+      var instance, test;
+
+      instance = this.createInstance();
+
+      test = instance.hash();
+      expect(test).to.be.a("SCInteger");
     });
     it("#<", function() {
       var instance, test;
diff --git a/src/sc/classlib/Core/Object.js b/src/sc/classlib/Core/Object.js
index a59c90f..6a461cc 100644
--- a/src/sc/classlib/Core/Object.js
+++ b/src/sc/classlib/Core/Object.js
@@ -231,9 +231,18 @@ SCScript.install(function(sc) {
     // TODO: implements equals
     // TODO: implements compareObject
     // TODO: implements instVarHash
-    // TODO: implements basicHash
-    // TODO: implements hash
-    // TODO: implements identityHash
+
+    spec.basicHash = function() {
+      return $SC.Integer(this._hash);
+    };
+
+    spec.hash = function() {
+      return $SC.Integer(this._hash);
+    };
+
+    spec.identityHash = function() {
+      return $SC.Integer(this._hash);
+    };
 
     spec["->"] = function($obj) {
       return $SC("Association").new(this, $obj);
diff --git a/src/sc/classlib/Core/Object_test.js b/src/sc/classlib/Core/Object_test.js
index 1537464..589adfd 100644
--- a/src/sc/classlib/Core/Object_test.js
+++ b/src/sc/classlib/Core/Object_test.js
@@ -481,11 +481,29 @@
     });
     it.skip("#instVarHash", function() {
     });
-    it.skip("#basicHash", function() {
+    it("#basicHash", function() {
+      var instance, test;
+
+      instance = this.createInstance();
+
+      test = instance.basicHash();
+      expect(test).to.be.a("SCInteger");
     });
-    it.skip("#hash", function() {
+    it("#hash", function() {
+      var instance, test;
+
+      instance = this.createInstance();
+
+      test = instance.hash();
+      expect(test).to.be.a("SCInteger");
     });
-    it.skip("#identityHash", function() {
+    it("#identityHash", function() {
+      var instance, test;
+
+      instance = this.createInstance();
+
+      test = instance.identityHash();
+      expect(test).to.be.a("SCInteger");
     });
     it("#->", sinon.test(function() {
       var instance, test, spy;
diff --git a/src/sc/classlib/Math/Integer.js b/src/sc/classlib/Math/Integer.js
index c9da6f2..adf007c 100644
--- a/src/sc/classlib/Math/Integer.js
+++ b/src/sc/classlib/Math/Integer.js
@@ -48,7 +48,9 @@ SCScript.install(function(sc) {
 
     spec.isInteger = utils.alwaysReturn$true;
 
-    // TODO: implements hash
+    spec.hash = function() {
+      return $SC.Float(this._).hash();
+    };
 
     [
       [ "+", $SC.Integer, $SC.Float ],
diff --git a/src/sc/classlib/Math/Integer_test.js b/src/sc/classlib/Math/Integer_test.js
index e284f13..a78db7d 100644
--- a/src/sc/classlib/Math/Integer_test.js
+++ b/src/sc/classlib/Math/Integer_test.js
@@ -51,7 +51,13 @@
         [ Infinity, [], false ],
       ]);
     });
-    it.skip("#hash", function() {
+    it("#hash", function() {
+      var instance, test;
+
+      instance = this.createInstance();
+
+      test = instance.hash();
+      expect(test).to.be.a("SCInteger");
     });
     it("#+", function() {
       testCase(this, [
diff --git a/src/sc/classlib/Math/Magnitude.js b/src/sc/classlib/Math/Magnitude.js
index f395ba1..9acda53 100644
--- a/src/sc/classlib/Math/Magnitude.js
+++ b/src/sc/classlib/Math/Magnitude.js
@@ -15,10 +15,6 @@ SCScript.install(function(sc) {
       return $SC.Boolean(this.valueOf() !== $aMagnitude.valueOf());
     };
 
-    spec.hash = function() {
-      return this._subclassResponsibility("hash");
-    };
-
     spec["<"] = function($aMagnitude) {
       return $SC.Boolean(this < $aMagnitude);
     };
diff --git a/src/sc/classlib/Math/Magnitude_test.js b/src/sc/classlib/Math/Magnitude_test.js
index c4f6ba9..7593999 100644
--- a/src/sc/classlib/Math/Magnitude_test.js
+++ b/src/sc/classlib/Math/Magnitude_test.js
@@ -32,12 +32,6 @@
         [ 3, [ 2 ], true  ],
       ]);
     });
-    it("#hash", function() {
-      var instance = this.createInstance();
-      expect(function() {
-        instance.hash();
-      }).to.throw(Error, "should have been implemented by subclass");
-    });
     it("#<", function() {
       testCase(this, [
         [ 1, [ 2 ], true  ],
diff --git a/src/sc/classlib/Math/SimpleNumber.js b/src/sc/classlib/Math/SimpleNumber.js
index 045eb6a..a43603f 100644
--- a/src/sc/classlib/Math/SimpleNumber.js
+++ b/src/sc/classlib/Math/SimpleNumber.js
@@ -434,8 +434,6 @@ SCScript.install(function(sc) {
       return this.absdif($that) ["<"] ($precision);
     }, "that; precision=0.0001");
 
-    // TODO: implements hash
-
     spec.asInteger = function() {
       return $SC.Integer(this._);
     };
diff --git a/src/sc/classlib/Math/SimpleNumber_test.js b/src/sc/classlib/Math/SimpleNumber_test.js
index 9b344dd..5cea111 100644
--- a/src/sc/classlib/Math/SimpleNumber_test.js
+++ b/src/sc/classlib/Math/SimpleNumber_test.js
@@ -625,8 +625,6 @@
         [ 10, [ 10.01, 0.02 ], true  ],
       ]);
     });
-    it.skip("#hash", function() {
-    });
     it("#asInteger", function() {
       testCase(this, [
         [ $SC.Integer(10), [], $SC.Integer(10) ],
diff --git a/src/sc/lang/klass/klass.js b/src/sc/lang/klass/klass.js
index 71ec008..64e6a95 100644
--- a/src/sc/lang/klass/klass.js
+++ b/src/sc/lang/klass/klass.js
@@ -10,6 +10,7 @@
   var klass       = {};
   var metaClasses = {};
   var classes     = klass.classes = {};
+  var hash = 0x100000;
 
   var createClassInstance = function(MetaSpec) {
     var instance = new SCClass();
@@ -46,7 +47,9 @@
             className + bond + methodName + " is already defined."
         );
       }
-      methods[methodName] = func;
+      Object.defineProperty(methods, methodName, {
+        value: func, writable: true
+      });
     };
 
     if (typeof fn === "function") {
@@ -113,9 +116,11 @@
     newClass = new MetaClass._MetaSpec();
     newClass._name = className;
     newClass._Spec = constructor;
-    constructor.prototype.__class = newClass;
-    constructor.prototype.__Spec  = constructor;
-    constructor.prototype.__className = className;
+    Object.defineProperties(constructor.prototype, {
+      __class: { value: newClass, writable: true },
+      __Spec : { value: constructor },
+      __className: { value: className }
+    });
     classes[className] = newClass;
 
     return newClass;
@@ -196,6 +201,9 @@
     Object.defineProperties(this, {
       _immutable: {
         value: false, writable: true
+      },
+      _hash: {
+        value: hash++
       }
     });
   }
diff --git a/src/sc/test/utils.js b/src/sc/test/utils.js
index 6c67738..9466cdd 100644
--- a/src/sc/test/utils.js
+++ b/src/sc/test/utils.js
@@ -272,8 +272,6 @@
     return instance;
   };
 
-  var __testid = Date.now();
-
   sc.test.object = function(properties) {
     var instance = sc.lang.klass.classes.Object.new();
 
@@ -284,7 +282,7 @@
         });
       });
     }
-    instance.__testid = __testid++;
+    instance.__testid = instance._hash;
 
     return instance;
   };