C# 创建将T约束到枚举的泛型方法
我正在构建一个函数来扩展C# 创建将T约束到枚举的泛型方法,c#,generics,enums,generic-constraints,C#,Generics,Enums,Generic Constraints,我正在构建一个函数来扩展Enum.Parse概念 允许在找不到枚举值的情况下解析默认值 不区分大小写 所以我写了以下内容： public static T GetEnumFromString<T>(string value, T defaultValue) where T : Enum { if (string.IsNullOrEmpty(value)) return defaultValue; foreach (T item in Enum.GetValues(
Enum.Parse- 允许在找不到枚举值的情况下解析默认值
- 不区分大小写
public static T GetEnumFromString<T>(string value, T defaultValue) where T : Enum
{
if (string.IsNullOrEmpty(value)) return defaultValue;
foreach (T item in Enum.GetValues(typeof(T)))
{
if (item.ToString().ToLower().Equals(value.Trim().ToLower())) return item;
}
return defaultValue;
}
public static TValue ParseEnum<TValue>(string value, TValue defaultValue)
where TValue : struct // enum
{
try
{
if (String.IsNullOrEmpty(value))
return defaultValue;
return (TValue)Enum.Parse(typeof (TValue), value);
}
catch(Exception ex)
{
return defaultValue;
}
}
公共静态TValue ParseEnum（字符串值，TValue defaultValue）
其中TValue:struct//enum
{
尝试
{
if（String.IsNullOrEmpty（value））
返回默认值；
return（TValue）Enum.Parse（typeof（TValue），value）；
}
捕获（例外情况除外）
{
返回默认值；
}
}
public static T ParseEnum<T>(string enumString)
where T : struct // enum
{
if (String.IsNullOrEmpty(enumString) || !typeof(T).IsEnum)
throw new Exception("Type given must be an Enum");
try
{
return (T)Enum.Parse(typeof(T), enumString, true);
}
catch (Exception ex)
{
return default(T);
}
}
public static T ParseEnum（字符串enumString）
其中T:struct//enum
{
if（String.IsNullOrEmpty（enumString）| |！typeof（T.IsEnum）
抛出新异常（“给定的类型必须是枚举”）；
尝试
{
返回（T）Enum.Parse（typeof（T），enumString，true）；
}
捕获（例外情况除外）
{
返回默认值（T）；
}
}
内部密封的类GenericTypeThat requiresEnum{
需要Nenum（）的静态泛型类型{
if（！typeof（T）.IsEnum）{
抛出新ArgumentException（“T必须是枚举类型”）；
}
}
}
然后在parse方法中，您可以使用Enum.parse（typeof（T），input，true）将字符串转换为Enum。最后一个true参数用于忽略输入的大小写 由于
EnumIConvertiblepublic T GetEnumFromString<T>(string value) where T : struct, IConvertible
{
if (!typeof(T).IsEnum)
{
throw new ArgumentException("T must be an enumerated type");
}
//...
}
public T GetEnumFromString（字符串值），其中T:struct，IConvertible
{
if（！typeof（T）.IsEnum）
{
抛出新ArgumentException（“T必须是枚举类型”）；
}
//...
}
这仍然允许传递实现
IConvertible有趣的是，这显然是（管理C++，IL直接）。 引述：
。。。这两个约束实际上都产生了有效的IL，并且如果用另一种语言编写（也可以在托管C++或IL中声明这些约束），也可以被C语言消耗。谁知道呢我确实有特定的要求，我需要使用带有与枚举值关联的文本的枚举。例如，当我使用enum指定错误类型时，它需要描述错误详细信息
public static class XmlEnumExtension
{
public static string ReadXmlEnumAttribute(this Enum value)
{
if (value == null) throw new ArgumentNullException("value");
var attribs = (XmlEnumAttribute[]) value.GetType().GetField(value.ToString()).GetCustomAttributes(typeof (XmlEnumAttribute), true);
return attribs.Length > 0 ? attribs[0].Name : value.ToString();
}
public static T ParseXmlEnumAttribute<T>(this string str)
{
foreach (T item in Enum.GetValues(typeof(T)))
{
var attribs = (XmlEnumAttribute[])item.GetType().GetField(item.ToString()).GetCustomAttributes(typeof(XmlEnumAttribute), true);
if(attribs.Length > 0 && attribs[0].Name.Equals(str)) return item;
}
return (T)Enum.Parse(typeof(T), str, true);
}
}
public enum MyEnum
{
[XmlEnum("First Value")]
One,
[XmlEnum("Second Value")]
Two,
Three
}
static void Main()
{
// Parsing from XmlEnum attribute
var str = "Second Value";
var me = str.ParseXmlEnumAttribute<MyEnum>();
System.Console.WriteLine(me.ReadXmlEnumAttribute());
// Parsing without XmlEnum
str = "Three";
me = str.ParseXmlEnumAttribute<MyEnum>();
System.Console.WriteLine(me.ReadXmlEnumAttribute());
me = MyEnum.One;
System.Console.WriteLine(me.ReadXmlEnumAttribute());
}
公共静态类XmlEnumExtension
{
公共静态字符串ReadXmlEnumAttribute（此枚举值）
{
如果（value==null）抛出新的ArgumentNullException（“value”）；
var attribs=（XmlEnumAttribute[]）value.GetType（）.GetField（value.ToString（））.GetCustomAttributes（typeof（XmlEnumAttribute），true）；
返回attribs.Length>0？attribs[0]。名称：value.ToString（）；
}
公共静态T ParseXmlEnumAttribute（此字符串str）
{
foreach（Enum.GetValues中的T项（typeof（T）））
{
var attribs=（XmlEnumAttribute[]）item.GetType（）.GetField（item.ToString（））.GetCustomAttributes（typeof（XmlEnumAttribute），true）；
如果（attribs.Length>0&&attribs[0].Name.Equals（str））返回项；
}
返回（T）Enum.Parse（typeof（T），str，true）；
}
}
公共枚举髓鞘
{
[XmlEnum（“第一个值”）]
一,，
[XmlEnum（“第二个值”）]
二,，
三
}
静态void Main（）
{
//从XmlEnum属性解析
var str=“第二个值”；
var me=str.ParseXmlEnumAttribute（）；
System.Console.WriteLine（me.ReadXmlEnumAttribute（））；
//无XmlEnum解析
str=“三”；
me=str.ParseXmlEnumAttribute（）；
System.Console.WriteLine（me.ReadXmlEnumAttribute（））；
me=MyEnum.1；
System.Console.WriteLine（me.ReadXmlEnumAttribute（））；
}
public静态IEnumerable GetEnumValues（）
{
类型enumType=typeof（TEnum）；
如果（！enumType.IsEnum）
抛出新ArgumentException（“类型参数必须是枚举类型”）；
数组enumValues=Enum.GetValues（enumType）；
返回enumValues.Cast（）；
}
public T LoadEnum<T>(string value, T defaultValue = default(T)) where T : struct, IComparable, IFormattable, IConvertible
{
if (Enum.IsDefined(typeof(T), value))
{
return (T)Enum.Parse(typeof(T), value, true);
}
return defaultValue;
}
public T LoadEnum（字符串值，T defaultValue=default（T）），其中T:struct，IComparable，IFormattable，IConvertible
{
如果（枚举已定义（类型（T），值））
{
返回（T）Enum.Parse（typeof（T），value，true）；
}
返回默认值；
}
public static Dictionary<int, string> EnumNamedValues<T>() where T : System.Enum
{
var result = new Dictionary<int, string>();
var values = Enum.GetValues(typeof(T));
foreach (int item in values)
result.Add(item, Enum.GetName(typeof(T), item));
return result;
}
System.Enum.assembly MyThing{}ilasm.exe /DLL /OUTPUT=MyThing.netmodule
public T LoadEnum<T>(string value, T defaultValue = default(T)) where T : struct, IComparable, IFormattable, IConvertible
{
if (Enum.IsDefined(typeof(T), value))
{
return (T)Enum.Parse(typeof(T), value, true);
}
return defaultValue;
}
public static Dictionary<int, string> EnumNamedValues<T>() where T : System.Enum
{
var result = new Dictionary<int, string>();
var values = Enum.GetValues(typeof(T));
foreach (int item in values)
result.Add(item, Enum.GetName(typeof(T), item));
return result;
}
// license: http://www.apache.org/licenses/LICENSE-2.0.html
.assembly MyThing{}
.class public abstract sealed MyThing.Thing
extends [mscorlib]System.Object
{
.method public static !!T GetEnumFromString<valuetype .ctor ([mscorlib]System.Enum) T>(string strValue,
!!T defaultValue) cil managed
{
.maxstack 2
.locals init ([0] !!T temp,
[1] !!T return_value,
[2] class [mscorlib]System.Collections.IEnumerator enumerator,
[3] class [mscorlib]System.IDisposable disposer)
// if(string.IsNullOrEmpty(strValue)) return defaultValue;
ldarg strValue
call bool [mscorlib]System.String::IsNullOrEmpty(string)
brfalse.s HASVALUE
br RETURNDEF // return default it empty
// foreach (T item in Enum.GetValues(typeof(T)))
HASVALUE:
// Enum.GetValues.GetEnumerator()
ldtoken !!T
call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
call class [mscorlib]System.Array [mscorlib]System.Enum::GetValues(class [mscorlib]System.Type)
callvirt instance class [mscorlib]System.Collections.IEnumerator [mscorlib]System.Array::GetEnumerator()
stloc enumerator
.try
{
CONDITION:
ldloc enumerator
callvirt instance bool [mscorlib]System.Collections.IEnumerator::MoveNext()
brfalse.s LEAVE
STATEMENTS:
// T item = (T)Enumerator.Current
ldloc enumerator
callvirt instance object [mscorlib]System.Collections.IEnumerator::get_Current()
unbox.any !!T
stloc temp
ldloca.s temp
constrained. !!T
// if (item.ToString().ToLower().Equals(value.Trim().ToLower())) return item;
callvirt instance string [mscorlib]System.Object::ToString()
callvirt instance string [mscorlib]System.String::ToLower()
ldarg strValue
callvirt instance string [mscorlib]System.String::Trim()
callvirt instance string [mscorlib]System.String::ToLower()
callvirt instance bool [mscorlib]System.String::Equals(string)
brfalse.s CONDITION
ldloc temp
stloc return_value
leave.s RETURNVAL
LEAVE:
leave.s RETURNDEF
}
finally
{
// ArrayList's Enumerator may or may not inherit from IDisposable
ldloc enumerator
isinst [mscorlib]System.IDisposable
stloc.s disposer
ldloc.s disposer
ldnull
ceq
brtrue.s LEAVEFINALLY
ldloc.s disposer
callvirt instance void [mscorlib]System.IDisposable::Dispose()
LEAVEFINALLY:
endfinally
}
RETURNDEF:
ldarg defaultValue
stloc return_value
RETURNVAL:
ldloc return_value
ret
}
}
T GetEnumFromString<T>(string valueString, T defaultValue) where T : Enum
using MyThing;
// stuff...
private enum MyEnum { Yes, No, Okay }
static void Main(string[] args)
{
Thing.GetEnumFromString("No", MyEnum.Yes); // returns MyEnum.No
Thing.GetEnumFromString("Invalid", MyEnum.Okay); // returns MyEnum.Okay
Thing.GetEnumFromString("AnotherInvalid", 0); // compiler error, not an Enum
}
ilasm.exe /DLL /OUTPUT=MyThing.netmodule
// works, result is inferred to have type StringComparison
var result = MyThing.GetEnumFromString("OrdinalIgnoreCase", StringComparison.Ordinal);
// type restriction is recognized by C#, this fails at compile time
var result = MyThing.GetEnumFromString("OrdinalIgnoreCase", 42);
public static T GetEnumFromString<T>(string strValue, T defaultValue)
{
// Check if it realy enum at runtime
if (!typeof(T).IsEnum)
throw new ArgumentException("Method GetEnumFromString can be used with enums only");
if (!string.IsNullOrEmpty(strValue))
{
IEnumerator enumerator = Enum.GetValues(typeof(T)).GetEnumerator();
while (enumerator.MoveNext())
{
T temp = (T)enumerator.Current;
if (temp.ToString().ToLower().Equals(strValue.Trim().ToLower()))
return temp;
}
}
return defaultValue;
}
public abstract class ConstrainedEnumParser<TClass> where TClass : class
// value type constraint S ("TEnum") depends on reference type T ("TClass") [and on struct]
{
// internal constructor, to prevent this class from being inherited outside this code
internal ConstrainedEnumParser() {}
// Parse using pragmatic/adhoc hard cast:
// - struct + class = enum
// - 'guaranteed' call from derived <System.Enum>-constrained type EnumUtils
public static TEnum Parse<TEnum>(string value, bool ignoreCase = false) where TEnum : struct, TClass
{
return (TEnum)Enum.Parse(typeof(TEnum), value, ignoreCase);
}
public static bool TryParse<TEnum>(string value, out TEnum result, bool ignoreCase = false, TEnum defaultValue = default(TEnum)) where TEnum : struct, TClass // value type constraint S depending on T
{
var didParse = Enum.TryParse(value, ignoreCase, out result);
if (didParse == false)
{
result = defaultValue;
}
return didParse;
}
public static TEnum ParseOrDefault<TEnum>(string value, bool ignoreCase = false, TEnum defaultValue = default(TEnum)) where TEnum : struct, TClass // value type constraint S depending on T
{
if (string.IsNullOrEmpty(value)) { return defaultValue; }
TEnum result;
if (Enum.TryParse(value, ignoreCase, out result)) { return result; }
return defaultValue;
}
}
public class EnumUtils: ConstrainedEnumParser<System.Enum>
// reference type constraint to any <System.Enum>
{
// call to parse will then contain constraint to specific <System.Enum>-class
}
WeekDay parsedDayOrArgumentException = EnumUtils.Parse<WeekDay>("monday", ignoreCase:true);
WeekDay parsedDayOrDefault;
bool didParse = EnumUtils.TryParse<WeekDay>("clubs", out parsedDayOrDefault, ignoreCase:true);
parsedDayOrDefault = EnumUtils.ParseOrDefault<WeekDay>("friday", ignoreCase:true, defaultValue:WeekDay.Sunday);
public static class EnumUtils
{
public static TEnum ParseEnum<TEnum>(this string value,
bool ignoreCase = true,
TEnum defaultValue = default(TEnum))
where TEnum : struct, IComparable, IFormattable, IConvertible
{
if ( ! typeof(TEnum).IsEnum) { throw new ArgumentException("TEnum must be an enumerated type"); }
if (string.IsNullOrEmpty(value)) { return defaultValue; }
TEnum lResult;
if (Enum.TryParse(value, ignoreCase, out lResult)) { return lResult; }
return defaultValue;
}
}
using System;
internal static class EnumEnforcer
{
/// <summary>
/// Makes sure that generic input parameter is of an enumerated type.
/// </summary>
/// <typeparam name="T">Type that should be checked.</typeparam>
/// <param name="typeParameterName">Name of the type parameter.</param>
/// <param name="methodName">Name of the method which accepted the parameter.</param>
public static void EnforceIsEnum<T>(string typeParameterName, string methodName)
where T : struct, IConvertible
{
if (!typeof(T).IsEnum)
{
string message = string.Format(
"Generic parameter {0} in {1} method forces an enumerated type. Make sure your type parameter {0} is an enum.",
typeParameterName,
methodName);
throw new ArgumentException(message);
}
}
/// <summary>
/// Makes sure that generic input parameter is of an enumerated type.
/// </summary>
/// <typeparam name="T">Type that should be checked.</typeparam>
/// <param name="typeParameterName">Name of the type parameter.</param>
/// <param name="methodName">Name of the method which accepted the parameter.</param>
/// <param name="inputParameterName">Name of the input parameter of this page.</param>
public static void EnforceIsEnum<T>(string typeParameterName, string methodName, string inputParameterName)
where T : struct, IConvertible
{
if (!typeof(T).IsEnum)
{
string message = string.Format(
"Generic parameter {0} in {1} method forces an enumerated type. Make sure your input parameter {2} is of correct type.",
typeParameterName,
methodName,
inputParameterName);
throw new ArgumentException(message);
}
}
/// <summary>
/// Makes sure that generic input parameter is of an enumerated type.
/// </summary>
/// <typeparam name="T">Type that should be checked.</typeparam>
/// <param name="exceptionMessage">Message to show in case T is not an enum.</param>
public static void EnforceIsEnum<T>(string exceptionMessage)
where T : struct, IConvertible
{
if (!typeof(T).IsEnum)
{
throw new ArgumentException(exceptionMessage);
}
}
}
public static TEnum ParseToEnum<TEnum>(this string text) where TEnum : struct, IConvertible, IComparable, IFormattable
{
if (string.IsNullOrEmpty(text) || !typeof(TEnum).IsEnum)
throw new ArgumentException("TEnum must be an Enum type");
try
{
var enumValue = (TEnum)Enum.Parse(typeof(TEnum), text.Trim(), true);
return enumValue;
}
catch (Exception)
{
throw new ArgumentException(string.Format("{0} is not a member of the {1} enumeration.", text, typeof(TEnum).Name));
}
}
public static TEnum Parse<TEnum>(string value)
where TEnum : struct, Enum
{
...
}
public abstract class EnumClassUtils<TClass>
where TClass : class
{
public static TEnum Parse<TEnum>(string value)
where TEnum : struct, TClass
{
return (TEnum) Enum.Parse(typeof(TEnum), value);
}
}
public class EnumUtils : EnumClassUtils<Enum>
{
}
EnumUtils.Parse<SomeEnum>("value");
public static int ToInt<T>(this T soure) where T : IConvertible//enum
{
if (typeof(T).IsEnum)
{
return (int) (IConvertible)soure;// the tricky part
}
//else
// throw new ArgumentException("T must be an enumerated type");
return soure.ToInt32(CultureInfo.CurrentCulture);
}
MemberStatusEnum.Activated.ToInt()// using extension Method
(int) MemberStatusEnum.Activated //the ordinary way
public void MethodWithEnumConstraint<[EnumConstraint] T>() {...}
public void MethodWithTypeEnumConstraint<[EnumConstraint(typeof(ConsoleColor))] T>() {...}
public void MethodWithDelegateConstraint<[DelegateConstraint] T> ()
{...}
public void MethodWithTypeDelegateConstraint<[DelegateConstraint(typeof(Func<int>))] T> ()
{...}
public static class EnumUtils
{
public static Enum GetEnumFromString(string value, Enum defaultValue)
{
if (string.IsNullOrEmpty(value)) return defaultValue;
foreach (Enum item in Enum.GetValues(defaultValue.GetType()))
{
if (item.ToString().ToLower().Equals(value.Trim().ToLower())) return item;
}
return defaultValue;
}
}
var parsedOutput = (YourEnum)EnumUtils.GetEnumFromString(someString, YourEnum.DefaultValue);
public class MyGeneric<TEnum> where TEnum : System.Enum
{ }
public static Dictionary<int, string> EnumNamedValues<T>()
where T : System.Enum
{
var result = new Dictionary<int, string>();
var values = Enum.GetValues(typeof(T));
foreach (int item in values)
result.Add(item, Enum.GetName(typeof(T), item));
return result;
}
private static T GetEnumFromString<T>(string value, T defaultValue) where T : Enum
{
// Your code goes here...
}
import java.util.HashMap;
import java.util.Map;
import java.util.function.Function;
public class EnumFromString {
enum NumberEnum {One, Two, Three};
enum LetterEnum {A, B, C};
Map<String, Function<String, ? extends Enum>> enumsByName = new HashMap<>();
public static void main(String[] args) {
EnumFromString efs = new EnumFromString();
System.out.print("\nFirst string is NumberEnum.Two - enum is " + efs.acceptEnumeratedValue("NumberEnum.Two").name());
System.out.print("\nSecond string is LetterEnum.B - enum is " + efs.acceptEnumeratedValue("LetterEnum.B").name());
}
public EnumFromString() {
enumsByName.put("NumberEnum", s -> {return NumberEnum.valueOf(s);});
enumsByName.put("LetterEnum", s -> {return LetterEnum.valueOf(s);});
}
public Enum acceptEnumeratedValue(String enumDotValue) {
int pos = enumDotValue.indexOf(".");
String enumName = enumDotValue.substring(0, pos);
String value = enumDotValue.substring(pos + 1);
Enum enumeratedValue = enumsByName.get(enumName).apply(value);
return enumeratedValue;
}
}
public static class EnumExtensions
{
public static string GetDescription(this Enum @enum)
{
Type type = @enum.GetType();
FieldInfo fi = type.GetField(@enum.ToString());
DescriptionAttribute[] attrs =
fi.GetCustomAttributes(typeof(DescriptionAttribute), false) as DescriptionAttribute[];
if (attrs.Length > 0)
{
return attrs[0].Description;
}
return null;
}
}