Question

我写了这个方法：

static long Sum(params int[] numbers)
{
    long result = default(int);

    for (int i = 0; i < numbers.Length; i++)
        result += numbers[i];

    return result;
}

我调用了这样的方法：

Console.WriteLine(Sum(5, 1, 4, 10));
Console.WriteLine(Sum());  // this should be an error
Console.WriteLine(Sum(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15));

我希望编译器在没有任何参数（如Sum()）的情况下调用方法时显示错误。我怎么能这样做？

Answer 1

从params中提取第一个参数以使其成为强制性参数：

static long Sum(int firstSummand, params int[] numbers)

Answer 2

你可以写

 static long Sum(int number1, params int[] numbers)
 {
     long result = number1;
     ....
 }

但是你会丢失这个选项：

 int[] data = { 1, 2, 3 };
 long total = Sum(data);   // Error, but Sum(0, data) will work.

Answer 3

编辑：无法使用参数进行编译时间检查...这将为您提供运行时异常...

static long Sum(params int[] numbers)
{
    if(numbers == null || numbers.Length < 2)
    {
         throw new InvalidOperationException("You must provide at least two numbers to sum");
    }     

    long result = default(int);

    for (int i = 0; i < numbers.Length; i++)
         result += numbers[i];

    return result;
}

Answer 4

考虑两个重载：

static long Sum(int head, params int[] tail) {
  if (tail == null) throw new ArgumentNullException("tail");
  return Sum(new int[] { head }.Concat(tail));
}

static long Sum(IEnumerable<int> numbers) {
  if (numbers == null) throw new ArgumentNullException("numbers");
  long result = 0;
  foreach (var number in numbers) {
    result += number;
  }
  return result;
}

样本用法：

Console.WriteLine(Sum(5, 1, 4, 10));
//Console.WriteLine(Sum());  // Error: No overload for method 'Sum' takes 0 arguments
Console.WriteLine(Sum(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15));
int[] array = { 42, 43, 44 };
Console.WriteLine(Sum(array));

Answer 5

params至少需要一个参数作为array[] arguments的语法糖。你需要：

Sum(null);

并在您的方法中相应处理null个案。

用params的方法

5 个答案: