界面作为类型约束和界面作为参数的区别？ [英] Difference between interface as type constraint and interface as parameter?

问题描述

如果我想创建一个将 IList 的实例作为参数（或任何其他接口，但让我们使用 IList code>作为例子），我可以创建一个类型约束的泛型方法，例如：



  public static void Foo1< T>（T list）其中T：IList 
 {
 
} 
  

或者，我可以创建一个直接使用 IList 参数的方法：



  public static void Foo2（IList list）
 {
 
} 
  

对于所有的意图和目的，这些方法看起来像是完全一样：



  List< string> ; myList = new List< string>（）; 
 Foo1（myList）; 
 Foo2（myList）; 
  

这是我的问题 - 这两种方法有什么区别？看起来第二种方法更具可读性;是否还有其他差异我应该知道（不同的IL正在生成等）？


解决方案

有几点不同：



• 如果您再次需要 real 类型（例如传递给另一个泛型方法或记录），那么泛型方法会更好


• T 可能是一个值类型，但最终仍然以通用形式取消装箱。对于 IList 这种情况是不太可能的，但对于其他接口而言，这很可能是


• 通用形式允许您指定与实际对象类型不同的具体实现类型。例如，你可能传入一个空引用，但仍想知道哪个实现类型 T 是


• 有关详细信息，请参阅Joe Duffy的最近关于泛型的博客文章。

这实际上取决于你当然在做什么......除非你真的需要知道关于 T ，通用表单的唯一好处是装箱点。

If I wanted to create a method that takes an instance of IList as a parameter (or any other interface, but let's use IList as an example), I could create a generic method with a type constraint, e.g.:

public static void Foo1<T>(T list) where T : IList
{

}

Alternatively, I could create a method that takes an IList parameter directly:

public static void Foo2(IList list)
{

}

For all intents and purposes, it seems like these methods behave exactly the same:

List<string> myList = new List<string>();
Foo1(myList);
Foo2(myList);

So here's my question -- what's the difference between these two approaches? It seems like the second approach is slightly more readable; are there any other differences I should be aware of (different IL being generated, etc)? Thanks in advance.

解决方案

A couple of differences:

• If you ever need the real type again (e.g. to pass to another generic method or for logging) then the generic method will be better
• T could be a value type and still end up being unboxed in the generic form. It's pretty unlikely that this would be the case for IList, but for other interfaces it's highly plausible
• The generic form allows you to specify a concrete implementation type which is different from the actual object type. For example, you might pass in a null reference but still want to know which implementation type T is
• They will be JITted differently; see Joe Duffy's recent blog post on generics for more information

It really depends on what you're doing of course... unless you actually need to know anything about T within the method, the only benefit to the generic form is the boxing point.

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