c# – 为什么是通用函数成员选择非通用函数成员？

public enum EnumTest
{
    EnumEntry
}

public class TestClass
{
    public string FunctionMember(string s,EnumTest t = EnumTest.EnumEntry)
    {
        return "normal";
    }

    public string FunctionMember<T>(T t)
    {
        return "Generic";
    }
}

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

        Console.WriteLine(t.FunctionMember("a"));
    }
}

这将打印“通用”.删除,枚举t = EnumTest.EnumEntry使其打印“正常”.

而标准似乎很清楚,从14.4.2.2更好的功能成员第一个鉴别器应用是：

>如果MP和MQ之一是非通用的,而另一个是通用的,则非泛型更好.

我错过了一些或编译错误？

解决方法

你错过了一些东西这就是以下几点：

您使用一个参数调用该方法.只有一个方法有一个参数,一个是泛型​​的.那就是选择的那个.

只有当它没有找到匹配的方法时,才会看到具有可选参数的其他方法.

参考文献：

> C# 4.0 Specification,最后一段在21.4：

As a tie breaker rule,a function member for which all arguments where explicitly given is better than one for which default values were supplied in lieu of explicit arguments.

> MSDN,标题“超载分辨率”,最后一个项目符号：

If two candidates are judged to be equally good,preference goes to a candidate that does not have optional parameters for which arguments were omitted in the call. This is a consequence of a general preference in overload resolution for candidates that have fewer parameters.

> The C# Language Specification,“7.5.3.2更好的功能成员”一章：

Parameter lists for each of the candidate function members are constructed in the following way:

• The expanded form is used if the function member was applicable only in the expanded form.
• Optional parameters with no corresponding arguments are removed from the parameter list

它继续这样：

Given an argument list A with a set of argument expressions { E₁,E₂,…,E_N } and two applicable function members MP and MQ with parameter types { P₁,P₂,P_N } and { Q₁,Q₂,Q_N } […]

在这一点上,具有可选参数的方法已经不在游戏中. N为1,但该方法有两个参数.