如果有人需要通用 IsSet（可以改进开箱即用的创建），或者字符串到 Enum 的 onfly 转换（使用下面介绍的 EnumConstraint）：
public class TestClass
{ }
public struct TestStruct
{ }
public enum TestEnum
{
e1,
e2,
e3
}
public static class TestEnumConstraintExtenssion
{
public static bool IsSet<TEnum>(this TEnum _this, TEnum flag)
where TEnum : struct
{
return (((uint)Convert.ChangeType(_this, typeof(uint))) & ((uint)Convert.ChangeType(flag, typeof(uint)))) == ((uint)Convert.ChangeType(flag, typeof(uint)));
}
//public static TestClass ToTestClass(this string _this)
//{
// // #generates compile error (so no missuse)
// return EnumConstraint.TryParse<TestClass>(_this);
//}
//public static TestStruct ToTestStruct(this string _this)
//{
// // #generates compile error (so no missuse)
// return EnumConstraint.TryParse<TestStruct>(_this);
//}
public static TestEnum ToTestEnum(this string _this)
{
// #enum type works just fine (coding constraint to Enum type)
return EnumConstraint.TryParse<TestEnum>(_this);
}
public static void TestAll()
{
TestEnum t1 = "e3".ToTestEnum();
TestEnum t2 = "e2".ToTestEnum();
TestEnum t3 = "non existing".ToTestEnum(); // default(TestEnum) for non existing
bool b1 = t3.IsSet(TestEnum.e1); // you can ommit type
bool b2 = t3.IsSet<TestEnum>(TestEnum.e2); // you can specify explicite type
TestStruct t;
// #generates compile error (so no missuse)
//bool b3 = t.IsSet<TestEnum>(TestEnum.e1);
}
}
如果有人仍然需要 example hot 来创建 Enum 编码约束：
using System;
/// <summary>
/// would be same as EnumConstraint_T<Enum>Parse<EnumType>("Normal"),
/// but writen like this it abuses constrain inheritence on System.Enum.
/// </summary>
public class EnumConstraint : EnumConstraint_T<Enum>
{
}
/// <summary>
/// provides ability to constrain TEnum to System.Enum abusing constrain inheritence
/// </summary>
/// <typeparam name="TClass">should be System.Enum</typeparam>
public abstract class EnumConstraint_T<TClass>
where TClass : class
{
public static TEnum Parse<TEnum>(string value)
where TEnum : TClass
{
return (TEnum)Enum.Parse(typeof(TEnum), value);
}
public static bool TryParse<TEnum>(string value, out TEnum evalue)
where TEnum : struct, TClass // struct is required to ignore non nullable type error
{
evalue = default(TEnum);
return Enum.TryParse<TEnum>(value, out evalue);
}
public static TEnum TryParse<TEnum>(string value, TEnum defaultValue = default(TEnum))
where TEnum : struct, TClass // struct is required to ignore non nullable type error
{
Enum.TryParse<TEnum>(value, out defaultValue);
return defaultValue;
}
public static TEnum Parse<TEnum>(string value, TEnum defaultValue = default(TEnum))
where TEnum : struct, TClass // struct is required to ignore non nullable type error
{
TEnum result;
if (Enum.TryParse<TEnum>(value, out result))
return result;
return defaultValue;
}
public static TEnum Parse<TEnum>(ushort value)
{
return (TEnum)(object)value;
}
public static sbyte to_i1<TEnum>(TEnum value)
{
return (sbyte)(object)Convert.ChangeType(value, typeof(sbyte));
}
public static byte to_u1<TEnum>(TEnum value)
{
return (byte)(object)Convert.ChangeType(value, typeof(byte));
}
public static short to_i2<TEnum>(TEnum value)
{
return (short)(object)Convert.ChangeType(value, typeof(short));
}
public static ushort to_u2<TEnum>(TEnum value)
{
return (ushort)(object)Convert.ChangeType(value, typeof(ushort));
}
public static int to_i4<TEnum>(TEnum value)
{
return (int)(object)Convert.ChangeType(value, typeof(int));
}
public static uint to_u4<TEnum>(TEnum value)
{
return (uint)(object)Convert.ChangeType(value, typeof(uint));
}
}
希望这对某人有所帮助。