C＃不能调用重载的泛型方法非泛型方法 [英] C# cannot call overloaded non-generic method from generic method

问题描述

我有一个方法都有一些遗留代码的富有700重载：

I have some legacy code with a method foo which has 700+ overloads:

[DllImport("3rdparty.dll")]
protected static extern void foo(int len, ref structA obj);
[DllImport("3rdparty.dll")]
protected static extern void foo(int len, ref structB obj);
[DllImport("3rdparty.dll")]
protected static extern void foo(int len, ref structC obj);
//and 700 similar overloads for foo...

我想揭露通过一个单一的方法，这些重载的方法使用泛型：

I'd like to expose these overloaded methods through a single method using generics:

public void callFoo<T>(int len)
    where T : new()  //ensure an empty constructor so it can be activated
{
   T obj = Activator.CreateInstance<T>(); //foo expects obj to be empty, and fills it with data
   foo(len, ref obj);

   //...do stuff with obj...
}

不幸的是这将返回错误：的最佳重载方法匹配'富（INT，参考StructA）'有一些无效参数的和无法从参考T'转换以裁判StructA的。

Unfortunately this returns the errors: "The best overloaded method match for 'foo(int, ref StructA)' has some invalid arguments" and "cannot convert from 'ref T' to 'ref StructA'".

有一种优雅的方式来实现这一目标？

Is there an elegant way to achieve this?

推荐答案

我希望动态将有助于在这里，但它不喜欢的 REF 。无论如何，反思应该工作：

I was hoping that dynamic would help here, but it doesn't like the ref. Anyway, reflection should work:

public T callFoo<T>(int len)
    where T : new()  //ensure an empty constructor so it can be activated
{
   T obj = new T();
   GetType().GetMethod("foo", BindingFlags.Instance | BindingFlags.NonPublic,
       null,  new[] { typeof(int), typeof(T).MakeByRefType() }, null)
       .Invoke(this, new object[] { len, obj });
   return obj;
}

---

下面是优化版，只做一次的反映;应该是的多的速度：

class Test
{

    protected void foo(int len, ref classA obj){}
    protected void foo(int len, ref classB obj){  }
    protected void foo(int len, ref classC obj){}
    static readonly Dictionary<Type, Delegate> functions;
    delegate void MyDelegate<T>(Test arg0, int len, ref T obj);
    static Test()
    {
        functions = new Dictionary<Type, Delegate>();
        foreach (var method in typeof(Test).GetMethods(BindingFlags.NonPublic | BindingFlags.Instance))
        {
            if (method.Name != "foo") continue;
            var args = method.GetParameters();
            if (args.Length != 2 || args[0].ParameterType != typeof(int)) continue;
            var type = args[1].ParameterType.GetElementType();
            functions[type] = Delegate.CreateDelegate(
                typeof(MyDelegate<>).MakeGenericType(type), method);
        }
    }
    public T callFoo<T>(int len)
        where T : new()  //ensure an empty constructor so it can be activated
    {
        T obj = new T();
        Delegate function;
        if (!functions.TryGetValue(typeof(T), out function)) throw new NotSupportedException(
             "foo is not supported for " + typeof(T).Name);
        ((MyDelegate<T>)function)(this, len, ref obj);
        return obj;
    }
}

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