问一个==号的问题，高手来帮偶啊

Question

这段代码编译会错，书上也这么说，理由是，书上说，这段代码假定T支持==运算符。可是，我实在想不出来那个类型不支持==运算符。class AAA<T>
    {
        public int age;        public bool Compare(T t1, T t2)
        {
            if(t1 == t2)
            {
                return true;
            }
            return false;
        }
    }

Answer 1

string str = "aa";
            int i = 1;
            if (str == i)
            { }

Answer 2

class   AAA <T> 
        { 
                public   int   age;                 public   bool   Compare(T   t1,   T   t2) 
                { 
                        if(t1.Equals(t2)) 
                        { 
                                return   true; 
                        } 
                        return   false; 
                } 
        } 

Answer 3

class   AAA <T> 
        { 
                public   int   age;                 public   bool   Compare(T   t1,   T   t2) 
                { 
                        if(t1.Equals(t2)) 
                        { 
                                return   true; 
                        } 
                        return   false; 
                } 
        } 

Answer 4

你这个比较怪异
给你一个泛型的例子
public class SqlFilter<T>
    {
        private string _name = null;        public string Name
        {
            get { return _name; }
        }        public SqlFilter(string name)
        {
            _name = name;
        }        public static SqlExpression operator ==(SqlFilter<T> t, T value)
        {
            SqlExpression _exp = new SqlExpression(string.Format("{0} = '{1}'", t.Name, value.ToString()));
            return _exp;
        }        public static SqlExpression operator !=(SqlFilter<T> t, T value)
        {
            SqlExpression _exp = new SqlExpression(string.Format("{0} <> '{1}'", t.Name, value.ToString()));
            return _exp;
        }        public override int  GetHashCode()
        {
          return base.GetHashCode();
        }
    }