调用无参数构造函数后,具有引用类型成员的c#结构的Equality和gethashcode重写
我正在设计一个结构来比较来自两个不同来源的方法签名(目前使用调用无参数构造函数后,具有引用类型成员的c#结构的Equality和gethashcode重写,c#,.net,struct,clr,value-type,C#,.net,Struct,Clr,Value Type,我正在设计一个结构来比较来自两个不同来源的方法签名(目前使用System.Reflection直接从程序集获取它们)。因为我只关心唯一性,所以我选择了HashSet来存储我的结构,并使用subset方法比较它们 public struct MethodSignature : IEquatable<MethodSignature> { #region Immutable fields public readonly string AssemblyName; pu
System.Reflection
直接从程序集获取它们)。因为我只关心唯一性,所以我选择了HashSet
来存储我的结构,并使用subset方法比较它们
public struct MethodSignature : IEquatable<MethodSignature>
{
#region Immutable fields
public readonly string AssemblyName;
public readonly string ClassName;
public readonly string MethodName;
public readonly System.Type ReturnType;
public readonly Dictionary<string, System.Type> Parameters;
#endregion
#region Constructors
public MethodSignature(string assemblyName, string className, string methodName, Type returnType, Dictionary<string, System.Type> parameters)
{
AssemblyName = assemblyName;
ClassName = className;
MethodName = methodName;
ReturnType = returnType;
Parameters = parameters;
}
#endregion
#region public Methods
public override string ToString()
{
string paramts = GetParametersAsString();
return string.Format("{0} {1}::{2}.{3}({4})", ReturnType.ToString(), AssemblyName, ClassName, MethodName, paramts);
}
public static bool operator ==(MethodSignature signature1, MethodSignature signature2)
{
// No nasty null checking thanks to value types :D :D :D
return signature1.Equals(signature2);
}
public static bool operator !=(MethodSignature signature1, MethodSignature signature2)
{
// No nasty null checking thanks to value types :D :D :D
return !signature1.Equals(signature2);
}
public bool Equals(MethodSignature signature)
{
return AreMethodSignatureEquals(signature);
}
public override bool Equals(object obj)
{
if (obj is MethodSignature)
return Equals((MethodSignature)obj);
else
return false;
}
#endregion
#region private Members
private string GetParametersAsString()
{
StringBuilder sb = new StringBuilder();
foreach (KeyValuePair<string, System.Type> param in Parameters)
{
sb.Append(string.Format("{0} {1},", param.Value.ToString(), param.Key.ToString()));
}
//Remove trailing comma
sb.Length--;
return sb.ToString();
}
private bool AreMethodSignatureEquals(MethodSignature signature)
{
return (AreAssemblyNamesEqual(signature.AssemblyName)
&& AreClassNameEquals(signature.ClassName)
&& AreMethodNameEquals(signature.MethodName)
&& AreReturnTypeEquals(signature.ReturnType)
&& AreParametersEquals(signature.Parameters));
}
private bool AreParametersEquals(Dictionary<string, Type> parameters)
{
return parameters.Count == Parameters.Count
&& AreSameSizeDictionariesKeyValuePairsEqual(parameters);
}
private bool AreSameSizeDictionariesKeyValuePairsEqual(Dictionary<string, Type> parameters)
{
foreach (KeyValuePair<string, Type> param in Parameters)
{
Type paramType;
//TryGetValue returns true if finds the keyValuePair
if (parameters.TryGetValue(param.Key, out paramType))
{
if (AreParameterTypesDifferent(param.Value, paramType))
{
return false;
}
}
else
{
return false;
}
}
return true;
}
private static bool AreParameterTypesDifferent(Type typeParameter1, Type typeParameter2)
{
return !typeParameter2.Equals(typeParameter1);
}
private bool AreReturnTypeEquals(Type returnType)
{
return returnType.Equals(ReturnType);
}
private bool AreMethodNameEquals(string methodName)
{
// Ensuring case sensitive using IEquatable<string>
return methodName.Equals(MethodName);
}
private bool AreClassNameEquals(string className)
{
// Ensuring case sensitive using IEquatable<string>
return className.Equals(ClassName);
}
private bool AreAssemblyNamesEqual(string assemblyName)
{
// Ensuring case sensitive using IEquatable<string>
return assemblyName.Equals(AssemblyName);
}
#endregion
}
编译器没有抱怨,因为ms1和ms2被认为已初始化。我知道这是因为C#中的所有值类型默认都有一个无参数构造函数,默认为其所有成员。如果我将此行为与Microsoft提供的值类型进行比较
int a = new int();
int b = new int();
// Returns true
Console.WriteLine(a.Equals(b));
它们肯定是相等的,比较GetHashCode()
的两个返回值也会返回true
我已经检查过了,但是,我不知道如何为此结构创建符合GetHashCode概念的每个引用类型的默认值(两个相等的对象返回相等的哈希代码)
最后,我的问题是:
当使用默认无参数构造函数时,结构中存在引用类型时,如何重写符合IEquatable实现的GetHashCode(),由于所有字段均为
null
(它们都是引用类型),因此将出现异常。
如果您想要
MethodSignature ms1 = new MethodSignature();
MethodSignature ms2 = new MethodSignature();
要被视为平等,您应按如下方式调整代码:
private bool AreParametersEquals(Dictionary<string, Type> parameters)
{
if((parameters == null) && (Parameters == null)) return true;
if((parameters == null) || (Parameters == null)) return false;
if(parameters.Count != Parameters.Count) return false;
var paramArray1 = parameters.OrderBy(p => p.Key).ToArray();
var paramArray2 = Parameters.OrderBy(p => p.Key).ToArray();
for(int i = 0; i < paramArray1.Length; i++)
{
if(!string.Equals(paramArray1[i].Key, paramArray2[i].Key)) return false;
if(!string.Equals(paramArray1[i].Key, paramArray2[i].Key)) return false;
}
return true;
}
private bool AreReturnTypeEquals(Type returnType)
{
if((returnType == null) && (ReturnType == null)) return true;
return (returnType != null) && returnType.Equals(ReturnType);
}
private bool AreMethodNameEquals(string methodName)
{
// Ensuring case sensitive using IEquatable<string>
return string.Equals(methodName, MethodName);
}
private bool AreClassNameEquals(string className)
{
// Ensuring case sensitive using IEquatable<string>
return string.Equals(className, ClassName);
}
private bool AreAssemblyNamesEqual(string assemblyName)
{
// Ensuring case sensitive using IEquatable<string>
return string.Equals(assemblyName, AssemblyName);
}
此实现将使用字段的null
值,并为字段中具有完全相同值的不同实例返回相同的结果
注意:一旦使用此hashcode(例如,在
字典中存储MethodSignature
实例),您就不应该更改基础参数字典
,因为这将影响GetHashCode
计算。这个问题相当混乱;为什么不简单地使用=
来确定两个字符串是否相等?或者,如果您喜欢使用一个方法,静态String.Equals(s1,s2)
method?@EricLippert我知道,对于字符串,运算符==的重载考虑空实例,我也使用我的单元测试系统进行了检查。Type和Dictionary,==运算符正确处理空值!引用类型的运算符==也总是检查空引用吗?@monsiergutix:Yes==
对引用类型正确地检查空引用。也就是说,如果您在引用类型上重载了=
,那么您有责任为空操作数正确实现它。@EricLippert谢谢!因此,只需使用运算符==的IEquatable接口更改所有等式,就可以实现NullPointerException。要解决这个问题,为什么struct MethodSignature的GetHashCode()不会抱怨其中的引用类型默认为null?据我所知,GetHashCode没有检查空值…@monsiergutix:显然你的观点是错误的。为什么您认为默认的GetHashCode
不知道空值?如果((parameters==null)和&(parameters==null))返回true,我建议替换带有if(ReferenceEquals(参数,参数))的code>返回true代码>。这不仅处理“均为null”的情况,还处理“非null reference equals”的情况。如果引用是相等的,那么每一个其他的相等测试都会成功,所以这样做没有意义;请尽早离开。@JohanDonne非常感谢建议的GetHashCode实现!
private bool AreParametersEquals(Dictionary<string, Type> parameters)
{
if((parameters == null) && (Parameters == null)) return true;
if((parameters == null) || (Parameters == null)) return false;
if(parameters.Count != Parameters.Count) return false;
var paramArray1 = parameters.OrderBy(p => p.Key).ToArray();
var paramArray2 = Parameters.OrderBy(p => p.Key).ToArray();
for(int i = 0; i < paramArray1.Length; i++)
{
if(!string.Equals(paramArray1[i].Key, paramArray2[i].Key)) return false;
if(!string.Equals(paramArray1[i].Key, paramArray2[i].Key)) return false;
}
return true;
}
private bool AreReturnTypeEquals(Type returnType)
{
if((returnType == null) && (ReturnType == null)) return true;
return (returnType != null) && returnType.Equals(ReturnType);
}
private bool AreMethodNameEquals(string methodName)
{
// Ensuring case sensitive using IEquatable<string>
return string.Equals(methodName, MethodName);
}
private bool AreClassNameEquals(string className)
{
// Ensuring case sensitive using IEquatable<string>
return string.Equals(className, ClassName);
}
private bool AreAssemblyNamesEqual(string assemblyName)
{
// Ensuring case sensitive using IEquatable<string>
return string.Equals(assemblyName, AssemblyName);
}
public override int GetHashCode()
{
unchecked // Overflow is fine, just wrap
{
int hash = (int)2166136261;
// Suitable nullity checks etc, of course :)
hash = (hash * 16777619) ^ AssemblyName?.GetHashCode()??0;
hash = (hash * 16777619) ^ ClassName?.GetHashCode()??0;
hash = (hash * 16777619) ^ MethodName?.GetHashCode()??0;
hash = (hash * 16777619) ^ ReturnType?.GetHashCode()??0;
if(Parameters == null) return hash;
var paramArray = Parameters.OrderBy(p => p.Key).ToArray();
for(int i = 0; i < Parameters.Count; i++)
{
hash = (hash * 16777619) ^ paramArray[i].Key?.GetHashCode()??0;
hash = (hash * 16777619) ^ paramArray[i].Value?.GetHashCode()??0;
}
return hash;
}
}