c#比较两个泛型值
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c# compare two generic values
提问by bernhardrusch
Possible Duplicate:
Can't operator == be applied to generic types in C#?
可能的重复：
运算符 == 不能应用于 C# 中的泛型类型吗？
I've coded something like this:
我已经编写了这样的代码：
public bool IsDataChanged()
{
T value1 = GetValue2;
T value2 = GetValue1();
return (valueInDB != valueFromView);
}
Right now the function doesn't compile with the error "Operator '!=' cannot be applied to operands of type 'T' and 'T'". What do I have to do to make this function work ?
现在该函数无法编译并出现错误“运算符 '!=' 不能应用于类型为 'T' 和 'T' 的操作数”。我该怎么做才能使此功能正常工作？
采纳答案by ShuggyCoUk
You cannot use operators on generic types (except for foo == null which is special cased) unless you add where T : class to indicate it is a reference type (then foo == bar is legal)
您不能在泛型类型上使用运算符（除了 foo == null 这是特殊情况），除非您添加 where T : class 以指示它是引用类型（然后 foo == bar 是合法的）
Use EqualityComparer<T>.Default to do it for you. This will notwork on types which only supply an operator overload for == without also either:
使用EqualityComparer<T>.Default 为你做这件事。这不适用于只为 == 提供运算符重载的类型，而没有：
- implement
IEquatable<T> - overrides object.Equals()
- 实施
IEquatable<T> - 覆盖 object.Equals()
In general implementing the == operator and not also doing at least one of these would be a very bad idea anyway so this is not likely to be an issue.
一般来说，实现 == 运算符而不至少执行其中一个操作将是一个非常糟糕的主意，因此这不太可能成为问题。
public bool IsDataChanged<T>()
{
T value1 = GetValue2;
T value2 = GetValue1();
return !EqualityComparer<T>.Default.Equals(value1 , value2);
}
If you do not restrict to IEquatable<T>then the EqualityComparer default fallback may cause boxing when used with value types if they do not implement IEquatable<T>(if you control the types which are being used this may not matter). I am assuming you were using =! for performance though so restricting to the Generic type will avoid accidentalboxing via the Object.Equals(object) route.
如果您不限制为，IEquatable<T>那么 EqualityComparer 默认回退可能会在与未实现的值类型一起使用时导致装箱IEquatable<T>（如果您控制正在使用的类型，这可能无关紧要）。我假设您正在使用 =！为了提高性能，因此限制为 Generic 类型将避免通过 Object.Equals(object) 路由意外装箱。
回答by CalvinR
That should work for you.
那应该对你有用。
public bool test<T>(T test, T test2) where T : class
{
return (test != test2);
}
This is simply pasted from the examples that were commented on your question.
这是从对您的问题发表评论的示例中简单粘贴的。
回答by Jay S
You can overload the .Equals() method on your objects and change your evaluation to:
您可以在对象上重载 .Equals() 方法并将评估更改为：
return (!valueInDB.Equals(valueFromView));
Assuming that valueInDB and valueFromView are objects. Your example variables aren't named the same as those used in the compare, so I had to assume.
假设 valueInDB 和 valueFromView 是对象。您的示例变量的名称与比较中使用的变量名称不同，因此我不得不假设。
EDIT: Got beat by 3 seconds! A note on overloading, if you need to compare values within a type, the basic .Equals() from the Object class won't be enough, as it will only do a memory compare for complex types. You'll need to overload and provide the implementation of how you want the object to be compared.
编辑：被击败了 3 秒！关于重载的注意事项，如果您需要比较一个类型中的值，来自 Object 类的基本 .Equals() 是不够的，因为它只会对复杂类型进行内存比较。您需要重载并提供您希望如何比较对象的实现。
回答by devio
Your type needs to implement the IComparableor IEquatableinterface.
您的类型需要实现IComparable或IEquatable接口。
Probably you then need to rewrite a!=b as !(a==b), or call the CompareTo() or Equals() method explicitly.
可能您随后需要将 a!=b 重写为 !(a==b)，或者显式调用 CompareTo() 或 Equals() 方法。
