有人能告诉我是否有一种方法可以用泛型将泛型类型参数T限制为:
Int16 Int32 Int64 UInt16 UInt32 UInt64
我知道哪里关键字，但不能找到只有这些类型的接口，
喜欢的东西:
static bool IntegerFunction<T>(T value) where T : INumeric
当前回答
如果你使用的是。net 4.0或更高版本，那么你可以使用dynamic作为方法参数，并在运行时检查传递的动态参数类型是数字/整数类型。
如果传递的动态类型不是数字/整数类型，则抛出异常。
实现这一想法的简短代码示例如下:
using System;
public class InvalidArgumentException : Exception
{
public InvalidArgumentException(string message) : base(message) {}
}
public class InvalidArgumentTypeException : InvalidArgumentException
{
public InvalidArgumentTypeException(string message) : base(message) {}
}
public class ArgumentTypeNotIntegerException : InvalidArgumentTypeException
{
public ArgumentTypeNotIntegerException(string message) : base(message) {}
}
public static class Program
{
private static bool IntegerFunction(dynamic n)
{
if (n.GetType() != typeof(Int16) &&
n.GetType() != typeof(Int32) &&
n.GetType() != typeof(Int64) &&
n.GetType() != typeof(UInt16) &&
n.GetType() != typeof(UInt32) &&
n.GetType() != typeof(UInt64))
throw new ArgumentTypeNotIntegerException("argument type is not integer type");
//code that implements IntegerFunction goes here
}
private static void Main()
{
Console.WriteLine("{0}",IntegerFunction(0)); //Compiles, no run time error and first line of output buffer is either "True" or "False" depends on the code that implements "Program.IntegerFunction" static method.
Console.WriteLine("{0}",IntegerFunction("string")); //Also compiles but it is run time error and exception of type "ArgumentTypeNotIntegerException" is thrown here.
Console.WriteLine("This is the last Console.WriteLine output"); //Never reached and executed due the run time error and the exception thrown on the second line of Program.Main static method.
}
当然，这个解决方案只能在运行时工作，而不能在编译时工作。
如果你想要一个总是在编译时工作而不在运行时工作的解决方案，那么你必须用一个公共结构/类来包装动态，它的重载公共构造函数只接受所需类型的参数，并给结构/类适当的名称。
被包装的动态总是类/结构的私有成员，它是结构/类的唯一成员，结构/类的唯一成员的名字是“value”，这是有意义的。
如果需要，还必须定义和实现公共方法和/或操作符，这些方法和/或操作符用于类/结构的私有动态成员的所需类型。
同样有意义的是，结构/类有特殊的/唯一的构造函数，它接受dynamic作为参数，初始化它唯一的私有动态成员“value”，但这个构造函数的修饰符当然是私有的。
类/结构准备好后，将参数的IntegerFunction类型定义为已定义的类/结构。
实现这个想法的长代码示例如下:
using System;
public struct Integer
{
private dynamic value;
private Integer(dynamic n) { this.value = n; }
public Integer(Int16 n) { this.value = n; }
public Integer(Int32 n) { this.value = n; }
public Integer(Int64 n) { this.value = n; }
public Integer(UInt16 n) { this.value = n; }
public Integer(UInt32 n) { this.value = n; }
public Integer(UInt64 n) { this.value = n; }
public Integer(Integer n) { this.value = n.value; }
public static implicit operator Int16(Integer n) { return n.value; }
public static implicit operator Int32(Integer n) { return n.value; }
public static implicit operator Int64(Integer n) { return n.value; }
public static implicit operator UInt16(Integer n) { return n.value; }
public static implicit operator UInt32(Integer n) { return n.value; }
public static implicit operator UInt64(Integer n) { return n.value; }
public static Integer operator +(Integer x, Int16 y) { return new Integer(x.value + y); }
public static Integer operator +(Integer x, Int32 y) { return new Integer(x.value + y); }
public static Integer operator +(Integer x, Int64 y) { return new Integer(x.value + y); }
public static Integer operator +(Integer x, UInt16 y) { return new Integer(x.value + y); }
public static Integer operator +(Integer x, UInt32 y) { return new Integer(x.value + y); }
public static Integer operator +(Integer x, UInt64 y) { return new Integer(x.value + y); }
public static Integer operator -(Integer x, Int16 y) { return new Integer(x.value - y); }
public static Integer operator -(Integer x, Int32 y) { return new Integer(x.value - y); }
public static Integer operator -(Integer x, Int64 y) { return new Integer(x.value - y); }
public static Integer operator -(Integer x, UInt16 y) { return new Integer(x.value - y); }
public static Integer operator -(Integer x, UInt32 y) { return new Integer(x.value - y); }
public static Integer operator -(Integer x, UInt64 y) { return new Integer(x.value - y); }
public static Integer operator *(Integer x, Int16 y) { return new Integer(x.value * y); }
public static Integer operator *(Integer x, Int32 y) { return new Integer(x.value * y); }
public static Integer operator *(Integer x, Int64 y) { return new Integer(x.value * y); }
public static Integer operator *(Integer x, UInt16 y) { return new Integer(x.value * y); }
public static Integer operator *(Integer x, UInt32 y) { return new Integer(x.value * y); }
public static Integer operator *(Integer x, UInt64 y) { return new Integer(x.value * y); }
public static Integer operator /(Integer x, Int16 y) { return new Integer(x.value / y); }
public static Integer operator /(Integer x, Int32 y) { return new Integer(x.value / y); }
public static Integer operator /(Integer x, Int64 y) { return new Integer(x.value / y); }
public static Integer operator /(Integer x, UInt16 y) { return new Integer(x.value / y); }
public static Integer operator /(Integer x, UInt32 y) { return new Integer(x.value / y); }
public static Integer operator /(Integer x, UInt64 y) { return new Integer(x.value / y); }
public static Integer operator %(Integer x, Int16 y) { return new Integer(x.value % y); }
public static Integer operator %(Integer x, Int32 y) { return new Integer(x.value % y); }
public static Integer operator %(Integer x, Int64 y) { return new Integer(x.value % y); }
public static Integer operator %(Integer x, UInt16 y) { return new Integer(x.value % y); }
public static Integer operator %(Integer x, UInt32 y) { return new Integer(x.value % y); }
public static Integer operator %(Integer x, UInt64 y) { return new Integer(x.value % y); }
public static Integer operator +(Integer x, Integer y) { return new Integer(x.value + y.value); }
public static Integer operator -(Integer x, Integer y) { return new Integer(x.value - y.value); }
public static Integer operator *(Integer x, Integer y) { return new Integer(x.value * y.value); }
public static Integer operator /(Integer x, Integer y) { return new Integer(x.value / y.value); }
public static Integer operator %(Integer x, Integer y) { return new Integer(x.value % y.value); }
public static bool operator ==(Integer x, Int16 y) { return x.value == y; }
public static bool operator !=(Integer x, Int16 y) { return x.value != y; }
public static bool operator ==(Integer x, Int32 y) { return x.value == y; }
public static bool operator !=(Integer x, Int32 y) { return x.value != y; }
public static bool operator ==(Integer x, Int64 y) { return x.value == y; }
public static bool operator !=(Integer x, Int64 y) { return x.value != y; }
public static bool operator ==(Integer x, UInt16 y) { return x.value == y; }
public static bool operator !=(Integer x, UInt16 y) { return x.value != y; }
public static bool operator ==(Integer x, UInt32 y) { return x.value == y; }
public static bool operator !=(Integer x, UInt32 y) { return x.value != y; }
public static bool operator ==(Integer x, UInt64 y) { return x.value == y; }
public static bool operator !=(Integer x, UInt64 y) { return x.value != y; }
public static bool operator ==(Integer x, Integer y) { return x.value == y.value; }
public static bool operator !=(Integer x, Integer y) { return x.value != y.value; }
public override bool Equals(object obj) { return this == (Integer)obj; }
public override int GetHashCode() { return this.value.GetHashCode(); }
public override string ToString() { return this.value.ToString(); }
public static bool operator >(Integer x, Int16 y) { return x.value > y; }
public static bool operator <(Integer x, Int16 y) { return x.value < y; }
public static bool operator >(Integer x, Int32 y) { return x.value > y; }
public static bool operator <(Integer x, Int32 y) { return x.value < y; }
public static bool operator >(Integer x, Int64 y) { return x.value > y; }
public static bool operator <(Integer x, Int64 y) { return x.value < y; }
public static bool operator >(Integer x, UInt16 y) { return x.value > y; }
public static bool operator <(Integer x, UInt16 y) { return x.value < y; }
public static bool operator >(Integer x, UInt32 y) { return x.value > y; }
public static bool operator <(Integer x, UInt32 y) { return x.value < y; }
public static bool operator >(Integer x, UInt64 y) { return x.value > y; }
public static bool operator <(Integer x, UInt64 y) { return x.value < y; }
public static bool operator >(Integer x, Integer y) { return x.value > y.value; }
public static bool operator <(Integer x, Integer y) { return x.value < y.value; }
public static bool operator >=(Integer x, Int16 y) { return x.value >= y; }
public static bool operator <=(Integer x, Int16 y) { return x.value <= y; }
public static bool operator >=(Integer x, Int32 y) { return x.value >= y; }
public static bool operator <=(Integer x, Int32 y) { return x.value <= y; }
public static bool operator >=(Integer x, Int64 y) { return x.value >= y; }
public static bool operator <=(Integer x, Int64 y) { return x.value <= y; }
public static bool operator >=(Integer x, UInt16 y) { return x.value >= y; }
public static bool operator <=(Integer x, UInt16 y) { return x.value <= y; }
public static bool operator >=(Integer x, UInt32 y) { return x.value >= y; }
public static bool operator <=(Integer x, UInt32 y) { return x.value <= y; }
public static bool operator >=(Integer x, UInt64 y) { return x.value >= y; }
public static bool operator <=(Integer x, UInt64 y) { return x.value <= y; }
public static bool operator >=(Integer x, Integer y) { return x.value >= y.value; }
public static bool operator <=(Integer x, Integer y) { return x.value <= y.value; }
public static Integer operator +(Int16 x, Integer y) { return new Integer(x + y.value); }
public static Integer operator +(Int32 x, Integer y) { return new Integer(x + y.value); }
public static Integer operator +(Int64 x, Integer y) { return new Integer(x + y.value); }
public static Integer operator +(UInt16 x, Integer y) { return new Integer(x + y.value); }
public static Integer operator +(UInt32 x, Integer y) { return new Integer(x + y.value); }
public static Integer operator +(UInt64 x, Integer y) { return new Integer(x + y.value); }
public static Integer operator -(Int16 x, Integer y) { return new Integer(x - y.value); }
public static Integer operator -(Int32 x, Integer y) { return new Integer(x - y.value); }
public static Integer operator -(Int64 x, Integer y) { return new Integer(x - y.value); }
public static Integer operator -(UInt16 x, Integer y) { return new Integer(x - y.value); }
public static Integer operator -(UInt32 x, Integer y) { return new Integer(x - y.value); }
public static Integer operator -(UInt64 x, Integer y) { return new Integer(x - y.value); }
public static Integer operator *(Int16 x, Integer y) { return new Integer(x * y.value); }
public static Integer operator *(Int32 x, Integer y) { return new Integer(x * y.value); }
public static Integer operator *(Int64 x, Integer y) { return new Integer(x * y.value); }
public static Integer operator *(UInt16 x, Integer y) { return new Integer(x * y.value); }
public static Integer operator *(UInt32 x, Integer y) { return new Integer(x * y.value); }
public static Integer operator *(UInt64 x, Integer y) { return new Integer(x * y.value); }
public static Integer operator /(Int16 x, Integer y) { return new Integer(x / y.value); }
public static Integer operator /(Int32 x, Integer y) { return new Integer(x / y.value); }
public static Integer operator /(Int64 x, Integer y) { return new Integer(x / y.value); }
public static Integer operator /(UInt16 x, Integer y) { return new Integer(x / y.value); }
public static Integer operator /(UInt32 x, Integer y) { return new Integer(x / y.value); }
public static Integer operator /(UInt64 x, Integer y) { return new Integer(x / y.value); }
public static Integer operator %(Int16 x, Integer y) { return new Integer(x % y.value); }
public static Integer operator %(Int32 x, Integer y) { return new Integer(x % y.value); }
public static Integer operator %(Int64 x, Integer y) { return new Integer(x % y.value); }
public static Integer operator %(UInt16 x, Integer y) { return new Integer(x % y.value); }
public static Integer operator %(UInt32 x, Integer y) { return new Integer(x % y.value); }
public static Integer operator %(UInt64 x, Integer y) { return new Integer(x % y.value); }
public static bool operator ==(Int16 x, Integer y) { return x == y.value; }
public static bool operator !=(Int16 x, Integer y) { return x != y.value; }
public static bool operator ==(Int32 x, Integer y) { return x == y.value; }
public static bool operator !=(Int32 x, Integer y) { return x != y.value; }
public static bool operator ==(Int64 x, Integer y) { return x == y.value; }
public static bool operator !=(Int64 x, Integer y) { return x != y.value; }
public static bool operator ==(UInt16 x, Integer y) { return x == y.value; }
public static bool operator !=(UInt16 x, Integer y) { return x != y.value; }
public static bool operator ==(UInt32 x, Integer y) { return x == y.value; }
public static bool operator !=(UInt32 x, Integer y) { return x != y.value; }
public static bool operator ==(UInt64 x, Integer y) { return x == y.value; }
public static bool operator !=(UInt64 x, Integer y) { return x != y.value; }
public static bool operator >(Int16 x, Integer y) { return x > y.value; }
public static bool operator <(Int16 x, Integer y) { return x < y.value; }
public static bool operator >(Int32 x, Integer y) { return x > y.value; }
public static bool operator <(Int32 x, Integer y) { return x < y.value; }
public static bool operator >(Int64 x, Integer y) { return x > y.value; }
public static bool operator <(Int64 x, Integer y) { return x < y.value; }
public static bool operator >(UInt16 x, Integer y) { return x > y.value; }
public static bool operator <(UInt16 x, Integer y) { return x < y.value; }
public static bool operator >(UInt32 x, Integer y) { return x > y.value; }
public static bool operator <(UInt32 x, Integer y) { return x < y.value; }
public static bool operator >(UInt64 x, Integer y) { return x > y.value; }
public static bool operator <(UInt64 x, Integer y) { return x < y.value; }
public static bool operator >=(Int16 x, Integer y) { return x >= y.value; }
public static bool operator <=(Int16 x, Integer y) { return x <= y.value; }
public static bool operator >=(Int32 x, Integer y) { return x >= y.value; }
public static bool operator <=(Int32 x, Integer y) { return x <= y.value; }
public static bool operator >=(Int64 x, Integer y) { return x >= y.value; }
public static bool operator <=(Int64 x, Integer y) { return x <= y.value; }
public static bool operator >=(UInt16 x, Integer y) { return x >= y.value; }
public static bool operator <=(UInt16 x, Integer y) { return x <= y.value; }
public static bool operator >=(UInt32 x, Integer y) { return x >= y.value; }
public static bool operator <=(UInt32 x, Integer y) { return x <= y.value; }
public static bool operator >=(UInt64 x, Integer y) { return x >= y.value; }
public static bool operator <=(UInt64 x, Integer y) { return x <= y.value; }
}
public static class Program
{
private static bool IntegerFunction(Integer n)
{
//code that implements IntegerFunction goes here
//note that there is NO code that checks the type of n in rum time, because it is NOT needed anymore
}
private static void Main()
{
Console.WriteLine("{0}",IntegerFunction(0)); //compile error: there is no overloaded METHOD for objects of type "int" and no implicit conversion from any object, including "int", to "Integer" is known.
Console.WriteLine("{0}",IntegerFunction(new Integer(0))); //both compiles and no run time error
Console.WriteLine("{0}",IntegerFunction("string")); //compile error: there is no overloaded METHOD for objects of type "string" and no implicit conversion from any object, including "string", to "Integer" is known.
Console.WriteLine("{0}",IntegerFunction(new Integer("string"))); //compile error: there is no overloaded CONSTRUCTOR for objects of type "string"
}
}
注意，为了在你的代码中使用动态，你必须添加引用到微软。CSharp
如果. net框架的版本低于/低于/小于4.0，并且动态在该版本中未定义，那么你将不得不使用对象来代替，并将其转换为整数类型，这很麻烦，所以我建议你至少使用。net 4.0或更新版本，如果可以的话，这样你就可以使用动态而不是对象。
其他回答
不幸的是，在这种情况下，只能在where子句中指定struct。不能具体指定Int16、Int32等，这看起来确实很奇怪，但我相信，在决定不允许在where子句中使用值类型的基础上，有一些深层的实现原因。
我想唯一的解决方案是执行运行时检查，这不幸地阻止了在编译时拾取问题。大概是这样的:-
static bool IntegerFunction<T>(T value) where T : struct {
if (typeof(T) != typeof(Int16) &&
typeof(T) != typeof(Int32) &&
typeof(T) != typeof(Int64) &&
typeof(T) != typeof(UInt16) &&
typeof(T) != typeof(UInt32) &&
typeof(T) != typeof(UInt64)) {
throw new ArgumentException(
string.Format("Type '{0}' is not valid.", typeof(T).ToString()));
}
// Rest of code...
}
我知道这有点难看，但至少提供了所需的约束条件。
我还将研究此实现可能的性能影响，也许有更快的方法。
十多年后，这个特性终于出现在。net 7中。最通用的接口是INumber<TSelf>而不是innumeric(在系统中。数字名称空间)，它不仅包含整数类型。要只接受整数类型，可以考虑使用IBinaryInteger<TSelf>。以你的原型，神秘的IntegerFunction为例:
static bool IntegerFunction<T>(T value) where T : IBinaryInteger<T> {
return value > T.Zero;
}
Console.WriteLine(IntegerFunction(5)); // True
Console.WriteLine(IntegerFunction((sbyte)-5)); // False
Console.WriteLine(IntegerFunction((ulong)5)); // True
下面的答案(现在已经过时了)是作为一个历史的角度。
c#不支持这一点。在接受Bruce Eckel的采访时，Hejlsberg描述了没有实现该功能的原因:
And it's not clear that the added complexity is worth the small yield that you get. If something you want to do is not directly supported in the constraint system, you can do it with a factory pattern. You could have a Matrix<T>, for example, and in that Matrix you would like to define a dot product method. That of course that means you ultimately need to understand how to multiply two Ts, but you can't say that as a constraint, at least not if T is int, double, or float. But what you could do is have your Matrix take as an argument a Calculator<T>, and in Calculator<T>, have a method called multiply. You go implement that and you pass it to the Matrix.
然而，这会导致相当复杂的代码，用户必须为他们想要使用的每个T提供自己的Calculator<T>实现。只要它不需要是可扩展的，也就是说，如果你只想支持固定数量的类型，比如int和double，你可以使用一个相对简单的接口:
var mat = new Matrix<int>(w, h);
(GitHub Gist中的最小实现。)
然而，一旦您希望用户能够提供他们自己的自定义类型，您就需要打开这个实现，以便用户能够提供他们自己的Calculator实例。例如，要实例化一个使用自定义十进制浮点数实现DFP的矩阵，你必须编写以下代码:
var mat = new Matrix<DFP>(DfpCalculator.Instance, w, h);
实现DfpCalculator的所有成员:ICalculator<DFP>。
正如Sergey Shandar的回答中所讨论的那样，另一种选择(不幸的是，它也有同样的局限性)是使用策略类。
目前还没有“好的”解决方案。但是，您可以显著地缩小类型参数，以排除许多与您假设的“INumeric”约束不匹配的情况，如上面haacks所示。
static bool IntegerFunction<T>(T值)where T: IComparable, iformatable, IConvertible, IComparable<T>， IEquatable<T>， struct {…
考虑到这个问题的受欢迎程度和这样一个函数背后的兴趣，我很惊讶地看到，还没有涉及T4的答案。
在这个示例代码中，我将演示一个非常简单的示例，说明如何使用强大的模板引擎来完成编译器在幕后使用泛型所做的工作。
你可以简单地为你喜欢的每种类型生成你想要的函数，并相应地使用它(在编译时!)，而不是通过循环和牺牲编译时的确定性。
为了做到这一点:
创建一个新的名为GenericNumberMethodTemplate.tt的文本模板文件。 删除自动生成的代码(您将保留大部分代码，但有些代码不需要)。 添加以下片段:
<#@ template language="C#" #>
<#@ output extension=".cs" #>
<#@ assembly name="System.Core" #>
<# Type[] types = new[] {
typeof(Int16), typeof(Int32), typeof(Int64),
typeof(UInt16), typeof(UInt32), typeof(UInt64)
};
#>
using System;
public static class MaxMath {
<# foreach (var type in types) {
#>
public static <#= type.Name #> Max (<#= type.Name #> val1, <#= type.Name #> val2) {
return val1 > val2 ? val1 : val2;
}
<#
} #>
}
就是这样。你现在完成了。
保存这个文件会自动编译成这个源文件:
using System;
public static class MaxMath {
public static Int16 Max (Int16 val1, Int16 val2) {
return val1 > val2 ? val1 : val2;
}
public static Int32 Max (Int32 val1, Int32 val2) {
return val1 > val2 ? val1 : val2;
}
public static Int64 Max (Int64 val1, Int64 val2) {
return val1 > val2 ? val1 : val2;
}
public static UInt16 Max (UInt16 val1, UInt16 val2) {
return val1 > val2 ? val1 : val2;
}
public static UInt32 Max (UInt32 val1, UInt32 val2) {
return val1 > val2 ? val1 : val2;
}
public static UInt64 Max (UInt64 val1, UInt64 val2) {
return val1 > val2 ? val1 : val2;
}
}
在main方法中，你可以验证你是否具有编译时确定性:
namespace TTTTTest
{
class Program
{
static void Main(string[] args)
{
long val1 = 5L;
long val2 = 10L;
Console.WriteLine(MaxMath.Max(val1, val2));
Console.Read();
}
}
}
我先说一句:不，这并没有违反DRY原则。DRY原则的存在是为了防止人们在多个地方复制代码，从而导致应用程序变得难以维护。
这里的情况完全不同:如果您想要更改，那么您只需更改模板(对于您的所有生成都是一个单一的源代码!)，然后就完成了。
为了将它与您自己的自定义定义一起使用，请向生成的代码添加一个名称空间声明(确保它与您将定义自己的实现的名称空间声明相同)，并将该类标记为partial。然后，将这些行添加到你的模板文件中，这样它就会被包含在最终的编译中:
<#@ import namespace="TheNameSpaceYouWillUse" #>
<#@ assembly name="$(TargetPath)" #>
说实话:这太酷了。
免责声明:这个示例受到了Kevin Hazzard和Jason Bock, Manning Publications在。net中的元编程的严重影响。
从c# 7.3开始，您可以使用更接近的非托管约束来指定类型形参是非指针、非空的非托管类型。
class SomeGeneric<T> where T : unmanaged
{
//...
}
非托管约束意味着结构约束，并且不能与结构或new()约束组合。
如果是以下类型之一，则该类型为非托管类型:
Sbyte、byte、short、ushort、int、uint、long、ulong、char、float、double、decimal或bool 任何enum类型 任何指针类型 任何只包含非托管类型字段的用户定义结构类型，在c# 7.3及更早版本中，都不是构造类型(至少包含一个类型参数的类型)。
为了进一步限制和消除没有实现IComparable的指针和用户定义类型add IComparable(但enum仍然派生自IComparable，因此通过添加IEquatable < T >来限制enum，您可以根据您的情况进一步添加额外的接口。Unmanaged可以让这个列表更短):
class SomeGeneric<T> where T : unmanaged, IComparable, IEquatable<T>
{
//...
}
但是这并没有阻止DateTime实例化。
