C# .NET泛型中重载运算符约束的解决方案
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原文地址: http://stackoverflow.com/questions/147646/
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Solution for overloaded operator constraint in .NET generics
提问by blackwing
What would I do if I want to have a generic method that only accepts types that have overloaded an operator, for instance the subtraction operator. I tried using an interface as a constraint but interfaces can't have operator overloading.
如果我想要一个只接受重载运算符的类型的泛型方法，例如减法运算符，我该怎么办。我尝试使用接口作为约束，但接口不能有运算符重载。
What is the best way to achieve this?
实现这一目标的最佳方法是什么？
采纳答案by Marc Gravell
There is no immediate answer; operators are static, and cannot be expressed in constraints - and the existing primatives don't implement any specific interface (contrast to IComparable[<T>] which can be used to emulate greater-than / less-than).
没有立即的答案；运算符是静态的，不能用约束来表达 - 并且现有的原语不实现任何特定的接口（与可用于模拟大于/小于的 IComparable[<T>] 形成对比）。
However; if you just want it to work, then in .NET 3.5 there are some options...
然而; 如果你只是想让它工作，那么在 .NET 3.5 中有一些选项......
I have put together a library herethat allows efficient and simple access to operators with generics - such as:
我在这里整理了一个库，允许高效且简单地访问具有泛型的运算符 - 例如：
T result = Operator.Add(first, second); // implicit <T>; here
It can be downloaded as part of MiscUtil
它可以作为MiscUtil 的一部分下载
Additionally, in C# 4.0, this becomes possible via dynamic:
此外，在 C# 4.0 中，这可以通过dynamic以下方式实现：
static T Add<T>(T x, T y) {
dynamic dx = x, dy = y;
return dx + dy;
}
I also had (at one point) a .NET 2.0 version, but that is less tested. The other option is to create an interface such as
我也有（曾经）一个 .NET 2.0 版本，但测试较少。另一种选择是创建一个接口，如
interface ICalc<T>
{
T Add(T,T)()
T Subtract(T,T)()
}
etc, but then you need to pass an ICalc<T>;through all the methods, which gets messy.
等等，但是你需要ICalc<T>;通过所有的方法，这会变得混乱。
回答by YellPika
I found that IL can actually handle this quite well. Ex.
我发现 IL 实际上可以很好地处理这个问题。前任。
ldarg.0
ldarg.1
add
ret
Compiled in a generic method, the code will run fine as long as a primitive type is specified. It may be possible to extend this to call operator functions on non-primitive types.
以泛型方法编译，只要指定了原始类型，代码就可以正常运行。可以将其扩展为在非原始类型上调用运算符函数。
See here.
见这里。
回答by ja72
There is a piece of code stolen from the internats that I use a lot for this. It looks for or builds using ILbasic arithmetic operators. It is all done within an Operation<T>generic class, and all you have to do is assign the required operation into a delegate. Like add = Operation<double>.Add.
有一段从内部人员那里偷来的代码，我为此经常使用它。它使用IL基本算术运算符查找或构建。这一切都在一个Operation<T>泛型类中完成，您所要做的就是将所需的操作分配给一个委托。喜欢add = Operation<double>.Add。
It is used like this:
它是这样使用的：
public struct MyPoint
{
public readonly double x, y;
public MyPoint(double x, double y) { this.x=x; this.y=y; }
// User types must have defined operators
public static MyPoint operator+(MyPoint a, MyPoint b)
{
return new MyPoint(a.x+b.x, a.y+b.y);
}
}
class Program
{
// Sample generic method using Operation<T>
public static T DoubleIt<T>(T a)
{
Func<T, T, T> add=Operation<T>.Add;
return add(a, a);
}
// Example of using generic math
static void Main(string[] args)
{
var x=DoubleIt(1); //add integers, x=2
var y=DoubleIt(Math.PI); //add doubles, y=6.2831853071795862
MyPoint P=new MyPoint(x, y);
var Q=DoubleIt(P); //add user types, Q=(4.0,12.566370614359172)
var s=DoubleIt("ABC"); //concatenate strings, s="ABCABC"
}
}
Operation<T>Source code courtesy of paste bin: http://pastebin.com/nuqdeY8z
Operation<T>源代码由粘贴箱提供：http: //pastebin.com/nuqdeY8z
with attribution below:
归属如下：
/* Copyright (C) 2007 The Trustees of Indiana University
*
* Use, modification and distribution is subject to the Boost Software
* License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
* http://www.boost.org/LICENSE_1_0.txt)
*
* Authors: Douglas Gregor
* Andrew Lumsdaine
*
* Url: http://www.osl.iu.edu/research/mpi.net/svn/
*
* This file provides the "Operations" class, which contains common
* reduction operations such as addition and multiplication for any
* type.
*
* This code was heavily influenced by Keith Farmer's
* Operator Overloading with Generics
* at http://www.codeproject.com/csharp/genericoperators.asp
*
* All MPI related code removed by ja72.
*/
