static void Equals<T>(T x,T y)
{
    return x == y;    //operator == can't be applied to type T
}

阅读规范(v3.0中的§2.2.4和v4.0中的§7.3.4)：

7.2.4 Binary operator overload resolution

An operation of the form x
op y,where op is an overloadable
binary operator,x is an expression of
type X,and y is an expression of type
Y,is processed as follows:

• The set of candidate user-defined operators
  provided by X and Y for the operation
  operator op(x,y) is determined. The
  set consists of the union of the
  candidate operators provided by X and
  the candidate operators provided by Y,
  each determined using the rules of
  §7.2.5. If X and Y are the same type,
  or if X and Y are derived from a
  common base type,then shared
  candidate operators only occur in the
  combined set once.

• If the set of
  candidate user-defined operators is
  not empty,then this becomes the set
  of candidate operators for the
  operation. Otherwise,the predefined
  binary operator op implementations,
  including their lifted forms,become
  the set of candidate operators for the
  operation. The predefined
  implementations of a given operator
  are specified in the description of
  the operator (§7.7 through §7.11).

• The overload resolution rules of §7.4.3 are applied to the set of candidate operators to select the best operator with respect to the argument list (x,y),and this operator becomes the result of the overload resolution process. If overload resolution fails to select a single best operator,a compile-time error occurs.

在第2步中,我认为应该应用这个预定义的实现：

bool operator ==(object x,object y);
bool operator !=(object x,object y);

因为C#中的所有内容都来自Object.如何在步骤3中发生编译时错误？在这种情况下,我认为“重载分辨率无法选择”是不可能的.

编辑当我实现这样的事情时,我的脑海里出现了这个问题：

class EnumComparer<TEnum> : IEqualityComparer<TEnum>
{
    public bool Equals(TEnum x,TEnum y)
    {
        return x == y;
    }
    public int GetHashCode(TEnum obj)
    {
        return (int)obj;
    }
}

恐怕我需要建立一个表达式,并以Equals方法动态调用它.