有趣的问题。该规范定义了Equals
和GetHashcode
(注意规范中的错字!)方法将针对相同类型的实例运行,但实现未定义。碰巧,当前的MS C#编译器使用幻数,如-1134271262
的种子和-1521134295
的乘数来实现此功能。但是不是规范的一部分。从理论上讲,这可能会在C#编译器版本之间发生根本性变化,并且仍然能够满足需要。所以,如果2个程序集不是由同一个编译器编译的,那么就没有保证。事实上,编译器每次编译时都会想到新的种子值,这是“有效的”(但不太可能)。
就我个人而言,我会看看使用IL或Expression
技术来做到这一点。使用Expression
相当容易地通过名称比较成员相似形状的对象。
有关信息,我也看了如何mcs
(Mono的编译器)实现GetHashCode
,并是不同;而不是种子和乘数,它使用种子,异或,乘数,移位和加数的组合。所以微软和Mono编译的同类型将有非常不同GetHashCode
。
static class Program {
static void Main() {
var obj = new { A = "abc", B = 123 };
System.Console.WriteLine(obj.GetHashCode());
}
}
- 单声道:-2077468848
- 微软:-617335881
基本上,我不认为你能保证这一点。
如何:
using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
class Foo
{
public string A { get; set; }
public int B; // note a field!
static void Main()
{
var obj1 = new { A = "abc", B = 123 };
var obj2 = new Foo { A = "abc", B = 123 };
Console.WriteLine(MemberwiseComparer.AreEquivalent(obj1, obj2)); // True
obj1 = new { A = "abc", B = 123 };
obj2 = new Foo { A = "abc", B = 456 };
Console.WriteLine(MemberwiseComparer.AreEquivalent(obj1, obj2)); // False
obj1 = new { A = "def", B = 123 };
obj2 = new Foo { A = "abc", B = 456 };
Console.WriteLine(MemberwiseComparer.AreEquivalent(obj1, obj2)); // False
}
}
public static class MemberwiseComparer
{
public static bool AreEquivalent(object x, object y)
{
// deal with nulls...
if (x == null) return y == null;
if (y == null) return false;
return AreEquivalentImpl((dynamic)x, (dynamic)y);
}
private static bool AreEquivalentImpl<TX, TY>(TX x, TY y)
{
return AreEquivalentCache<TX, TY>.Eval(x, y);
}
static class AreEquivalentCache<TX, TY>
{
static AreEquivalentCache()
{
const BindingFlags flags = BindingFlags.Public | BindingFlags.Instance;
var xMembers = typeof(TX).GetProperties(flags).Select(p => p.Name)
.Concat(typeof(TX).GetFields(flags).Select(f => f.Name));
var yMembers = typeof(TY).GetProperties(flags).Select(p => p.Name)
.Concat(typeof(TY).GetFields(flags).Select(f => f.Name));
var members = xMembers.Intersect(yMembers);
Expression body = null;
ParameterExpression x = Expression.Parameter(typeof(TX), "x"),
y = Expression.Parameter(typeof(TY), "y");
foreach (var member in members)
{
var thisTest = Expression.Equal(
Expression.PropertyOrField(x, member),
Expression.PropertyOrField(y, member));
body = body == null ? thisTest
: Expression.AndAlso(body, thisTest);
}
if (body == null) body = Expression.Constant(true);
func = Expression.Lambda<Func<TX, TY, bool>>(body, x, y).Compile();
}
private static readonly Func<TX, TY, bool> func;
public static bool Eval(TX x, TY y)
{
return func(x, y);
}
}
}
注:我添加了一个'基于Expression'-成员逐一比较器 - 可能是有用的 – 2013-05-13 09:00:51
辉煌,谢谢。 – 2013-05-13 11:15:59