通用擴展方法編譯器錯誤

Question

我想編寫一個編譯器無法在運行時解析的通用擴展方法，雖然Visual Studio的intellisense確實找到它。

編譯器錯誤是'SampleSolution.OtherGenericClass<SampleSolution.IGenericInterface<SampleSolution.ISimpleInterface>,SampleSolution.ISimpleInterface>' does not contain a definition for 'GenericExtensionMethod' and no extension method 'GenericExtensionMethod' accepting a first argument of type 'SampleSolution.OtherGenericClass<SampleSolution.IGenericInterface<SampleSolution.ISimpleInterface>,SampleSolution.ISimpleInterface>' could be found (are you missing a using directive or an assembly reference?)

這裏是最簡單的形式，一些示例代碼，我可以拿出能重現問題。我知道我可以在IOtherGenericInterface中添加GenericExtensionMethod，但我需要擴展方法，因爲它需要在IOtherGenericInterface實現之外。

public interface ISimpleInterface 
{ 

} 

public interface IGenericInterface<T> 
{ 

} 

public class GenericClass<T> : IGenericInterface<T> 
{ 

} 

public interface IOtherGenericInterface<TGenericDerived> 
{ 

} 

public class OtherGenericClass<TGenericInterface, TSimpleInterface> : 
    IOtherGenericInterface<TGenericInterface> 
    where TGenericInterface : IGenericInterface<TSimpleInterface> 
{ 

} 

public static class GenericExtensionMethods 
{ 
    public static IOtherGenericInterface<TGenericInterface> 
     GenericExtensionMethod<TGenericInterface, TSimple>(
      this IOtherGenericInterface<TGenericInterface> expect) 
     where TGenericInterface : IGenericInterface<TSimple> 
    { 
     return expect; 
    } 
} 

class Program 
{ 
    static void Main(string[] args) 
    { 
     var exp = new OtherGenericClass<IGenericInterface<ISimpleInterface>, 
             ISimpleInterface>(); 

     //exp.GenericExtensionMethod(); // This doesn't compile 
    } 
} 

Answer 1

它沒有足夠的信息來明確地解決了一般類型參數;你將不得不使用：

exp.GenericExtensionMethod<IGenericInterface<ISimpleInterface>, ISimpleInterface>(); 

特別要注意的是，where約束後分辨率驗證- 他們不參與決議本身 - 這樣的分辨率在所有它可以推斷是TGenericInterface。