为什么不能指定接口的静态方法？ [英] Why can't interfaces specify static methods?

问题描述

我知道这个问题已经被问了个遍，但我似乎无法找到足够好的答案。因此要清楚什么，我想知道，我将在两个问题分开这样的：

1. 为什么 T接口具有静态方法的签名？我会尽力抢占非回答询问为什么在世界上我想用下面这样做：我会希望能够调用静态 GetDbConnectionType（）在 SqliteCodeGenerator 和 MssqlCodeGenerator ：

    接口ICodeGenerator 
    {
    //这是我想是静态的方法：
   串GetDbConnectionType（）; 
   } 
    
   抽象类CodeGeneratorBase：ICodeGenerator 
    {
   公共抽象的字符串GetDbConnectionType（）; 
    
   公共无效GenerateSomeCode（StringBuilder的S）
    {
    s.AppendLine（无功富=新的+ GetDbConnectionType（）+（）;）; 
   } 
   } 
    
   类SqliteCodeGenerator：CodeGeneratorBase 
    {
   公众覆盖字符串GetDbConnectionType（）
    {
   返回SQLiteConnection ; 
   } 
   } 
    
   类MssqlCodeGenerator：CodeGeneratorBase 
    {
   公众覆盖字符串GetDbConnectionType（）
    {
   回报的SqlConnection ; 
   } 
   } 
     




2. 在另一方面，这是这第二个问题的事情，如果你知道一个很好的选择，以通过各种手段...

达到上述目标，那么

解决方案

假设你的可能的指定一个接口，一个类型必须有一个特定的静态方法......你会怎么称呼呢？多态性致力于通过的实例的 - 而静态成员明确的不的使用情况

现在，话虽如此，还有的有一个的情况是，我可以看到静态接口成员的工作：泛型类型。例如：

  //这是无效的代码... 
公共无效美孚< T>（）其中T：ICodeGenerator 
 {
字符串类型= T.GetDbConnectionType（）; 
} 
  

这将呼吁的的静态成员的具体的键入 T 。

我已经的博客更多有关此，但我怀疑的利益并不能证明的复杂性。

在替代品方面 - 通常你必须另一个接口，并有不同的类型，以实现该接口。行之有效在某些情况下，而不是在其他

I know this question has been asked over and over, but I can't seem to find good enough answers. So to make it clear what I'm trying to know, I'll split this in two questions:

1. Why can't interfaces have static method signatures? I'll try to preempt the non-answers asking why in the world I would want to do this with the following: I would want to be able to statically invoke GetDbConnectionType() on SqliteCodeGenerator and MssqlCodeGenerator:

   interface ICodeGenerator
   {
       // this is the method I would like to be static:
       string GetDbConnectionType();
   }
   
   abstract class CodeGeneratorBase : ICodeGenerator
   {
       public abstract string GetDbConnectionType();
   
       public void GenerateSomeCode(StringBuilder s)
       {
           s.AppendLine("var foo = new " + GetDbConnectionType() + "();");
       }
   }
   
   class SqliteCodeGenerator : CodeGeneratorBase
   {
       public override string GetDbConnectionType()
       {
           return "SQLiteConnection";
       }
   }
   
   class MssqlCodeGenerator : CodeGeneratorBase
   {
       public override string GetDbConnectionType()
       {
           return "SqlConnection";
       }
   }
   

2. On the other hand, and this is the matter of this second question, if you know of a good alternative to reach the aforementioned goal, then by all means...

解决方案

Suppose you could specify in an interface that a type had to have a particular static method... how would you call it? Polymorphism works through instances - whereas static members explicitly don't use instances.

Now, having said that, there's one situation in which I can see static interface members working: generic types. For example:

// This isn't valid code...
public void Foo<T>() where T : ICodeGenerator
{
    string type = T.GetDbConnectionType();
}

That would call the static member on the concrete type T.

I've blogged more about this, but I suspect the benefit doesn't justify the complexity.

In terms of alternatives - usually you'd have another interface, and have separate types to implement that interface. That works well in some contexts, but not in others.

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