覆盖IEquatable< T>当T是接口并且哈希码在派生类型之间不同时 [英] Overriding IEquatable<T> when T is an interface and hashcodes are different between derived types
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问题描述
我有分别实现接口 I 的 A 和 B 类.
公共接口I{int SomeInt {get;}布尔SomeBool {}浮动SomeFloat {get;}}公开课A:我{public int SomeInt {get;}公共布尔SomeBool {get;}公众持票人SomeFloat {get;}私有只读字符串_someARelatedStuff;//课程的其余部分...}B类:我{public int SomeInt {get;}公共布尔SomeBool {get;}公众持票人SomeFloat {get;}私有字符串readonly _someBRelatedStuff;私人双只读_someOtherBRelatedStuff;//课程的其余部分...} 有时候我想测试 A 和 B 之间的相等性(通常是在比较 A 列表和 B 时)基于它们的 I 属性( SomeInt ， SomeBool ， SomeFloat )的相等性，因此我实现了两者都使用 IEquatable< I> ，然后根据它们共享的 I 属性值比较它们.
问题在于我已经在A和B上都实现了 GetHashCode()的实现，该实现会产生不同的哈希值，因为我正在考虑其他成员.
B 不依赖 A ，因此我使用接口 I 进行比较，并且具有带有吸气剂的属性列表.
如果要实现一个类，则应始终确保两个相等的对象具有相同的哈希码.
这是否意味着每当一个类 A 想要实现接口 I ，并且我希望能够比较实现 I 的实例时，code>，我必须确保对 I 的所有实例以相同的方式计算哈希码，并且仅使用 I 属性?
当T是接口时，我确实不打算实现 IEquatable< T> ，但是我的选择是:
- 对基类使用常规继承-我宁愿在可能的情况下避免继承，并且如果B由于单一继承而需要从某个框架
C类派生，则此解决方案将不起作用 - 使用
A或B上的方法在A和B之间执行相等性检查-将创建代码重复 - 在
I中定义的I实例之间具有相等性检查方法-听起来像是最好的选择
我缺少任何选择吗?
解决方案
请考虑制作一个 IEqualityComparer<> 类以比较公共值.
我已将接口重命名为 ICommon 以提高可读性
公共接口ICommon{int SomeInt {get;}布尔SomeBool {}浮动SomeFloat {get;}}公共类CommonComparer:IEqualityComparer< ICommon>{公共布尔等于(ICommon x，ICommon y){返回x.SomeInt.Equals(y.SomeInt)&&x.SomeBool.Equals(y.SomeBool)&&x.SomeFloat.Equals(y.SomeFloat);}public int GetHashCode(ICommon obj){未检查{int hc = -1817952719;hc =(-1521134295)* hc + obj.SomeInt.GetHashCode();hc =(-1521134295)* hc + obj.SomeBool.GetHashCode();hc =(-1521134295)* hc + obj.SomeFloat.GetHashCode();返回hc;}}} 该程序可以区分两个列表中的相等项.
class程序{静态void Main(string [] args){var listA = new List< A>{新的A(1001，true，1.001f，"A1")，新A(1002，true，1.002f，"A2")，新的A(1003，false，1.003f，"A1")，新的A(1004，false，1.004f，"A4")};var listB = new List< B>{新的B(1001，true，1.001f，"B1"，2.5)，新的B(1002，false，1.002f，"B2"，2.8)，新的B(1003，true，1.003f，"B3"，2.9)，新的B(1004，false，1.004f，"B4"，2.9)};var common = Enumerable.Intersect(listA，listB，new CommonComparer()).OfType< ICommon>();Console.WriteLine($"{" SomeInt，-8} {" Bool，-6} {" SomeFloat，-10}"));foreach(共同的var项目){Console.WriteLine($"{item.SomeInt，-8} {item.SomeBool，-6} {item.SomeFloat，-10}"));}//SomeInt Bool SomeFloat//1001是1.001//1004错误1.004}} 和其余的代码定义
公共类A:ICommon，IEquatable< A>{静态只读CommonComparer比较器=新的CommonComparer();public int SomeInt {get;}公共布尔SomeBool {get;}公众持票人SomeFloat {get;}私有只读字符串_someARelatedStuff;//课程的其余部分...公共A(ICommon其他，字符串someARelatedStuff):this(other.SomeInt，other.SomeBool，other.SomeFloat，someARelatedStuff){}公共A(int someInt，bool someBool，float someFloat，字符串someARelatedStuff){this.SomeInt = someInt;this.SomeBool = someBool;this.SomeFloat = someFloat;this._someARelatedStuff = someARelatedStuff;}公共替代字符串ToString()=>_someARelatedStuff;#region IEquatable成员公共重写bool等于(object obj){如果(obj是另一个){返回等于(其他)；}返回false；}公共虚拟布尔等于(另一个){返回comparer.Equals(this，other)&&_someARelatedStuff.Equals(other._someARelatedStuff);}公共重写int GetHashCode(){未检查{int hc = comparer.GetHashCode(this);hc =(-1521134295)* hc + _someARelatedStuff.GetHashCode();返回hc;}}#endregion}公共类别B:ICommon，IEquatable B{静态只读CommonComparer比较器=新的CommonComparer();public int SomeInt {get;}公共布尔SomeBool {get;}公众持票人SomeFloat {get;}只读字符串_someBRelatedStuff;只读double _someOtherBRelatedStuff;//课程的其余部分...公共B(ICommon other，字符串someBRelatedStuff，double someOtherBRelatedStuff):this(other.SomeInt，other.SomeBool，other.SomeFloat，someBRelatedStuff，someOtherBRelatedStuff){}公共B(int someInt，bool someBool，float someFloat，字符串someBRelatedStuff，double someOtherBRelatedStuff){this.SomeInt = someInt;this.SomeBool = someBool;this.SomeFloat = someFloat;this._someBRelatedStuff = someBRelatedStuff;this._someOtherBRelatedStuff = someOtherBRelatedStuff;}公共替代字符串ToString()=>$"{_ someBRelatedStuff}，{_someOtherBRelatedStuff.ToString(" g4)}" ;;#region IEquatable成员公共重写bool等于(object obj){如果(obj是B其他){返回等于(其他)；}返回false；}公共虚拟布尔等于(B其他){返回comparer.Equals(this，other)&&_someBRelatedStuff.Equals(other._someBRelatedStuff)&&_someOtherBRelatedStuff.Equals(other._someOtherBRelatedStuff);}公共重写int GetHashCode(){未检查{int hc = comparer.GetHashCode(this);hc =(-1521134295)* hc + _someBRelatedStuff.GetHashCode();hc =(-1521134295)* hc + _someOtherBRelatedStuff.GetHashCode();返回hc;}}#endregion} I have A and B classes both implementing interface I.
public interface I
{
int SomeInt { get; }
bool SomeBool { get; }
float SomeFloat { get; }
}
public class A : I
{
public int SomeInt { get; }
public bool SomeBool { get; }
public float SomeFloat { get; }
private readonly string _someARelatedStuff;
// Rest of class...
}
public class B : I
{
public int SomeInt { get; }
public bool SomeBool { get; }
public float SomeFloat { get; }
private string readonly _someBRelatedStuff;
private double readonly _someOtherBRelatedStuff;
// Rest of class...
}
Sometimes I want to test equality between A and B (usually when comparing lists of A and lists of B) based on the equality of their I properties (SomeInt, SomeBool, SomeFloat), so I implemented IEquatable<I> on both and I compare them based on their shared I properties values.
The problem is that I already have an implementation for GetHashCode() on both A and B that produces different hashes because I'm taking into account additional members.
B does not depend on A so I use interface I to compare them and it has a list of properties with getters.
I read in a StackOverflow answer that:
If you are implementing a class, you should always make sure that two equal objects have the same hashcode.
So does that mean that everytime a class A want to be implement interface I, and I want to be able to compare instances that implement I, I have to make sure the hashcode is calculated in the same way for all instances of I and only use I properties?
I do feel like I'm not intended to implement IEquatable<T> when T is an interface, but my alternatives are:
- Using regular inheritance with a base class - I rather avoid inheritance when possible, and this solution won't work if B needs to derive from some framework
Cclass because of single inheritance - Implement equality checks between
AandBwith a method on eitherAorB- will create code duplication - Have an equality check method between
Iinstances defined inI- sounds like the best option
Are there any options that I'm missing?
解决方案
Consider making the a IEqualityComparer<> class to compare the common values.
I have renamed the interface to ICommon for readability
public interface ICommon
{
int SomeInt { get; }
bool SomeBool { get; }
float SomeFloat { get; }
}
public class CommonComparer : IEqualityComparer<ICommon>
{
public bool Equals(ICommon x, ICommon y)
{
return x.SomeInt.Equals(y.SomeInt)
&& x.SomeBool.Equals(y.SomeBool)
&& x.SomeFloat.Equals(y.SomeFloat);
}
public int GetHashCode(ICommon obj)
{
unchecked
{
int hc = -1817952719;
hc = (-1521134295)*hc + obj.SomeInt.GetHashCode();
hc = (-1521134295)*hc + obj.SomeBool.GetHashCode();
hc = (-1521134295)*hc + obj.SomeFloat.GetHashCode();
return hc;
}
}
}
and the program can distinguish between the equal items on two lists.
class Program
{
static void Main(string[] args)
{
var listA = new List<A>
{
new A(1001, true, 1.001f, "A1"),
new A(1002, true, 1.002f, "A2"),
new A(1003, false, 1.003f, "A1"),
new A(1004, false, 1.004f, "A4")
};
var listB = new List<B>
{
new B(1001, true, 1.001f, "B1", 2.5),
new B(1002, false, 1.002f, "B2", 2.8),
new B(1003, true, 1.003f, "B3", 2.9),
new B(1004, false, 1.004f, "B4", 2.9)
};
var common = Enumerable.Intersect(listA, listB, new CommonComparer()).OfType<ICommon>();
Console.WriteLine($"{"SomeInt",-8} {"Bool",-6} {"SomeFloat",-10}");
foreach (var item in common)
{
Console.WriteLine($"{item.SomeInt,-8} {item.SomeBool,-6} {item.SomeFloat,-10}");
}
//SomeInt Bool SomeFloat
//1001 True 1.001
//1004 False 1.004
}
}
and the rest of the code definitions
public class A : ICommon, IEquatable<A>
{
static readonly CommonComparer comparer = new CommonComparer();
public int SomeInt { get; }
public bool SomeBool { get; }
public float SomeFloat { get; }
private readonly string _someARelatedStuff;
// Rest of class...
public A(ICommon other, string someARelatedStuff)
: this(other.SomeInt, other.SomeBool, other.SomeFloat, someARelatedStuff)
{ }
public A(int someInt, bool someBool, float someFloat, string someARelatedStuff)
{
this.SomeInt = someInt;
this.SomeBool = someBool;
this.SomeFloat = someFloat;
this._someARelatedStuff = someARelatedStuff;
}
public override string ToString() => _someARelatedStuff;
#region IEquatable Members
public override bool Equals(object obj)
{
if (obj is A other)
{
return Equals(other);
}
return false;
}
public virtual bool Equals(A other)
{
return comparer.Equals(this, other)
&& _someARelatedStuff.Equals(other._someARelatedStuff);
}
public override int GetHashCode()
{
unchecked
{
int hc = comparer.GetHashCode(this);
hc = (-1521134295)*hc + _someARelatedStuff.GetHashCode();
return hc;
}
}
#endregion
}
public class B : ICommon, IEquatable<B>
{
static readonly CommonComparer comparer = new CommonComparer();
public int SomeInt { get; }
public bool SomeBool { get; }
public float SomeFloat { get; }
readonly string _someBRelatedStuff;
readonly double _someOtherBRelatedStuff;
// Rest of class...
public B(ICommon other, string someBRelatedStuff, double someOtherBRelatedStuff)
: this(other.SomeInt, other.SomeBool, other.SomeFloat, someBRelatedStuff, someOtherBRelatedStuff)
{ }
public B(int someInt, bool someBool, float someFloat, string someBRelatedStuff, double someOtherBRelatedStuff)
{
this.SomeInt = someInt;
this.SomeBool = someBool;
this.SomeFloat = someFloat;
this._someBRelatedStuff = someBRelatedStuff;
this._someOtherBRelatedStuff = someOtherBRelatedStuff;
}
public override string ToString() => $"{_someBRelatedStuff}, {_someOtherBRelatedStuff.ToString("g4")}";
#region IEquatable Members
public override bool Equals(object obj)
{
if (obj is B other)
{
return Equals(other);
}
return false;
}
public virtual bool Equals(B other)
{
return comparer.Equals(this, other)
&& _someBRelatedStuff.Equals(other._someBRelatedStuff)
&& _someOtherBRelatedStuff.Equals(other._someOtherBRelatedStuff);
}
public override int GetHashCode()
{
unchecked
{
int hc = comparer.GetHashCode(this);
hc = (-1521134295)*hc + _someBRelatedStuff.GetHashCode();
hc = (-1521134295)*hc + _someOtherBRelatedStuff.GetHashCode();
return hc;
}
}
#endregion
}
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