var metal; //top namespace
if (!metal) 
    metal = {};

/**
 * 継承
 * @param {Object} subClass 実クラス
 * @param {Object} superClass 親クラス
 */
metal.extend = function(subClass, superClass) {
    for (var prop in superClass.prototype) {
        subClass.prototype[prop] = superClass.prototype[prop];
    }
}