混合泛型方法和扩展方法方法

2023-09-03 16:43:38 作者：被撕碎了的回忆

我创建了 Class1.GetChild＆LT; T＆GT;（）其中T：DependencyObject的中的 lib1.dll 的组件扩展方法。在此之后，所有的组件依赖于的 lib1.dll 的没有编译错误：

I created the Class1.GetChild<T>() where T : DependencyObject extension method in lib1.dll assembly. After that, all assemblies that depends on lib1.dll failed to compile with error:

类型System.Windows.DependencyObject'是一个assemebly定义未引用。您必须添加一个引用组件 WindowsBase等等...

The type 'System.Windows.DependencyObject' is defined in an assemebly that is not referenced. You must add a reference to assembly 'WindowsBase' etc...

为什么要依赖程序需要的 WindowsBase 的，即使他们不使用 GetChild ？

Why dependent assemblies requires WindowsBase even if they don't use GetChild?

。

要重现（VS2010 .NET4）：

To reproduce (vs2010 .net4):

lib1.dll （引用的 WindowsBase 的）

namespace lib1
{
    public static class Class1
    {
        public static T GetChild<T>(this DependencyObject src) where T : DependencyObject
        {
            return default(T);
        }
    }

    public static class Class2
    {
        public static int SomeExtMethod(this string src)
        {
            return 0;
        }
    }
}

lib2.dll （引用的 LIB1 的而不是 WindowsBase 的）

lib2.dll (references lib1 but not WindowsBase)

using lib1;
class someClass
{
    void someFct()
    {
        "foo".SomeExtMethod(); // error: The type 'System.Windows.DependencyObject'
                // is defined in an assemebly that is not referenced. 
                // You must add a reference to assembly 'WindowsBase' etc..
    }
}

更新：的

Update:

我觉得有混合泛型方法和扩展方法时的definitly东西。我所要证明的问题，下面的示例所示：

I think there's definitly something when mixing generic methods and extension methods. I tried to demonstrate the issue in the following sample:

// lib0.dll
namespace lib0
{
    public class Class0 { }
}

// lib1.dll
using lib0;
namespace lib1
{
    public static class Class1
    {
        public static void methodA<T>() where T : Class0 { }    // A
        public static void methodB(Class0 e) { }                // B
        public static void methodC(this int src) { }            // C
    }

    public static class Class2
    {
        public static void methodD(this String s) { }
    }
}

// lib2.dll
using lib1;
class someClass
{
    void someFct()
    {
        Class2.methodD("");  // always compile successfully
        "".methodD();        // raise the 'must add reference to lib0' error depending on config. see details below.
    }
}

A，// B，// C - >编译确定

A, //B, //C -> compile ok

A，B，// C - >编译确定

// A，B，C - >编译确定

A，// B，C - >引发错误

A，B，C - >引发错误

// A 办法的methodA 的评论。正如达指出，类型推断可能发挥一定的作用。还是好奇，想知道来龙去脉。

//A means methodA is commented. As Damien pointed out, type inference might play some role. Still curious to know the ins and outs.