typed local vars.js

/*
  Shows that strongly typed vars is possible in js! And do not worry about speed. :) Robust type system is more important than yet another benchmark :P. And i'll plan to make deploy system which checks all types and removes all 'ugly' `with`. This code definitely should be complexer, but i keep it simple.
  P.S. `with` rulezzz
  P.P.S. As you see its too easy to make field of class strongly typed too.
*/

(function($G){
  if(Object.defineProperty && !{}.__defineGetter__)
  {
    Object.prototype.__defineGetter__ = function(name, _fn)
    {
      Object.defineProperty(this, name, {get: _fn});
    }
  };
  if(Object.defineProperty && !{}.__defineSetter__)
  {
    Object.prototype.__defineSetter__ = function(name, _fn)
    {
      Object.defineProperty(this, name, {set: _fn});
    }
  };

  var _typedVarWithImplictCast = function(varMap, name, Type)
  {
    var v;
    
    varMap.__defineGetter__(name, function(){ return v });
    varMap.__defineSetter__(name, function(nv){ v = Type(nv) }); // throws CastError if cast is impossible
  };
  
  var _typedVars = function(varMap)
  {
    if(varMap == null)
      varMap = {};
    
    if(varMap._defTypedVar == null)
    {
      var varNameToType = {};
      
      varMap._defTypedVar = function(name, Type, v)
      {
        if(varMap.hasOwnProperty(name))
        {
          if(varNameToType[name] !== Type)
            throw TypeError('redeclaration with different type');
            
          varMap[name] = v;  
        }
        else
        {  
          _typedVarWithImplictCast(varMap, name, Type);
          varNameToType[name] = Type;
          
          varMap[name] = v;
        }
      }
    }  
    
    return varMap;
  };
  
  // export
  $G._typedVars = _typedVars;
})(this);


// example
(function($G)
{
  _typedVars($G);
  
  _defTypedVar('foo', String, '123');
  
  foo = 234;
  
  console.log(foo + 2);
  
  (function(){with(_typedVars())
  {
    _defTypedVar('bar', Boolean, false);
    
    bar = 1;
    
    console.log(bar);
  }})();
})(this);