Function IIF, how to make it take 2N + 1 arguments of logical expressions?, C #

Question

In Visual Basic, there is this IIF Function, as in Crystal Report, etc ...

In C # itself, this function does not exist, but it is the same as doing something like this:

bool a = true;
string b = a ? "is_True" : "is_False";

But for the code to be a bit easier to read I wanted to do it as a function for C #, leaving it like this:

public static T IIf<T>(bool expression, T truePart, T falsePart)
{
     return expression ? truePart : falsePart;
}

Or to not operate with the real values ??can also be done using delegates, to access the necessary values:

public static T IIf<T>(bool expression, Func<T> truePart, Func<T> falsePart)
{
    return expression ? truePart() : falsePart();
}

So far this works well ...

---

But how can I modify this function so I can take 2N + 1 arguments?

(N - the number of logical expressions specified)

Example the desired result:

Each odd argument specifies a logical expression;

Each even argument specifies the value that is returned if the previous expression evaluates to true;

The last argument specifies the value that is returned if the previously evaluated logical expressions yielded false.

int value = IIf(Name = "Joel", 1, Name = "Peter", 2, Name = "Maria", 3, 4);

Can someone give me a hand with this?

Environment: C # - Visual Studio 2017

Answer 1

首先，如评论中所述，这是一个坏主意。较新版本的C＃已经支持模式匹配开关作为该语言的内置功能。用它。

其次，这是一个坏主意，因为API“ argument，case1，result1，case2，result2，...”的签名很难在C＃类型系统中表达。

如果我被迫实现这样的API，我建议使用元组：

public static R Switch<A, R>(
  A item, 
  R theDefault, 
  params (A, R)[] cases )
{
    foreach(var c in cases) 
        if (item.Equals(c.Item1))
            return c.Item2;
    return theDefault;
}

或者，制作有用的实用程序方法并使用它：

public static T FirstOrDefault(
  this IEnumerable<T> items,
  T theDefault,
  Func<T, bool> predicate)
{
    foreach(var i in items.Where(predicate))
      return i;
    return theDefault;
} 

public static R Switch<A, R>(
    A item, 
    R theDefault, 
    params (A, R)[] cases ) =>
  cases.FirstOrDefault(
    (item, theDefault),
    c => item.Equals(c.Item1)).Item2;

如果由于使用的是较旧版本的C＃而无法使用元组，则可以创建自己的对类型或使用键值对类型。

但是只是不要去那里。如果需要开关，请编写开关。如果您需要字典，请编写字典。