c# - 方法签名中的 ICollection[]

Question

我有以下代码。为什么它总是采用“take(ICollection a)”方法？我认为它自己的对象应该是 LinkedList 或 HashSet，所以它应该调用另外两个 take 方法。

class Program
{
    static void Main(string[] args)
    {
        Program p = new Program();

        ICollection<String>[] ary = { new LinkedList<String>(), new HashSet<String>() };

        foreach (ICollection<String> a in ary)
        {
            p.take(a);
        }

        for (int i = 0; i < ary.Length; i++)
        {
            p.take(ary[i]);
        }
    }


    public void take(HashSet<String> a)
    { }

    public void take(LinkedList<String> a)
    {}

    public void take(ICollection<string> a)
    { }
}

Answer 1

方法分派(dispatch)是基于变量类型完成的，而不是运行时类型。这在 C# 语言规范 7.5.3(重载解决方案)中有详细介绍 - 在整个部分中都没有建议使用变量的运行时类型。调度由编译器根据“参数表达式”处理:

Given an argument list A with a set of argument expressions { E1, E2, ..., EN } and two applicable function members MP and MQ with parameter types { P1, P2, ..., PN } and { Q1, Q2, ..., QN }, MP is defined to be a better function member than MQ if

• for each argument, the implicit conversion from EX to QX is not better than the implicit conversion from EX to PX, and

• for at least one argument, the conversion from EX to PX is better than the conversion from EX to QX.

如果你想让它动态调度，你可以通过 dynamic :

 foreach (ICollection<String> a in ary)
 {
     dynamic o = a;
     p.take(o);
 }

或者，更短的形式:

 foreach (dynamic a in ary)
 {
     p.take(a);
 }