Parser syntax for this pointers

class TestClass
{
    protected _field;
    protected _obj;

    public function func1(int value)
    {
        let  this->_obj->{this->_field} = value;
    }

    public function func2(int value)
   {
            var obj, field;
         let obj = this->_obj;
         let field = this->_field;
        let obj->{field} = value;
    }

}

any idea why func1 produces syntax error while func2 doesnt?