为什么不Funcs接受超过16个参数？ [英] Why don't Funcs accept more than 16 arguments?

问题描述

由于Javascript是我最熟练的语言，因此我熟悉将函数用作一等对象。我曾想过C＃缺乏这个功能，但后来我听说 Func 和 Action 和例如，你可以声明一个 Func ，我认为它是非常棒的。 c>，它连接两个字符串并在它们之间放置一个空格，如下所示：



  Func< string，string，string> concat =（a，b）=> a ++ b; 
  

我注意到当你输入



 函数功能< 
  

智能感知表明它有17个重载：

 委托System.Func< out TResult> 
委托System.Func<在T，out TResult> 
代表System.Func<在T1中，在T2中，out TResult> 
 ... snip ... 
委托System.Func   

这让我发笑。我查看了 MSDN文档 Func 再次笑了起来。这让我尝试用17个参数声明 Func 。它导致一个错误（使用泛型类型'System.Func< TResult>'需要1个类型参数）。

我同意，有一个接受16个以上参数的 Func 可能不是一个好主意。即使如此，这对于执行 Func 来说似乎也是一种非常方便的方式。它需要17个不同的重载记录。这是它真正需要知道的一切：最后一个类型参数是返回类型，并且它之前的所有类型参数都是参数类型。

如果我想用超过16个参数创建 Func ？为什么有一个限制呢？为什么C＃不能让你用任意数量的参数声明一个 Func ？

解决方案

您希望像C＃所缺少的可变类型参数。 C＃需要修改泛型的类型，因此，可能会出现令人讨厌的扩散 Func ， Action 和元组类型。

如果您是语言购物用户，此功能已添加到C ++ 11中，但您可能只需使用jQuery。 ： - ）

Since Javascript is the language that I am the most proficient at, I am familiar with using functions as first-class objects. I had thought that C# lacked this feature, but then I heard about Func and Action and delegate, which I think are pretty awesomesauce.

For example, you can declare a Func that concatenates two strings and puts a space between them like this:

Func<string, string, string> concat = (a,b) => a + " " + b;

I noticed that when you type

Func<

the IntelliSense shows that it has 17 overloads:

delegate System.Func<out TResult>
delegate System.Func<in T, out TResult>
delegate System.Func<in T1, in T2, out TResult>
...snip...
delegate System.Func<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12, in T13, in T14, in T15, in T16, out TResult>

That made me laugh. I looked at the MSDN docs for Func and laughed again. This made me try to declare a Func with 17 arguments. It causes an error (Using the generic type 'System.Func<TResult>' requires 1 type arguments).

I can agree that it's probably not a good idea to have a Func that accepts more than 16 arguments. Even so, this seems like a kludgy way for Func to be implemented. It requires 17 trivially different overloads to be documented. This is all it really should need to know: the last type parameter is the return type, and all the type parameters before it are the argument types.

So what could I do if I wanted to create a Func with more than 16 parameters? Why is there a limit anyway? Why can't C# just let you declare a Func with an arbitrary number of arguments?

解决方案

You're hoping for something like variadic type arguments which C# lacks. C# requires the arity of generic types to be fixed, therefore the heinous proliferation of Func, Action, and Tuple types.

If you're language shopping, this feature was added in C++11, but you should probably just use jQuery. :-)

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