C＃6的改进重载 - 澄清？ [英] C#6's Improved overload resolution - clarification?

问题描述

在所有的C＃6，最神秘的功能（对我）的新功能是的改进重载的

Among all the new features in C#6, the most mysterious feature (to me) is the "improved overload resolution".

也许是因为我的找不到的相关信息/例子/它的解释。

Maybe it's because I couldn't find related info/examples/explanation about it.

没有讨论的唯一剩余的两个功能是定义
A自定义添加扩展方法帮助集合初始化支持，
和一些小的改进，但重载

The only two remaining features not discussed are support for defining a custom Add extension method to help with collection initializers, and some minor but improved overload resolution

综观的roslyn维基的

有一些小的改进重载决议，其中
很可能会导致更多的事情只是工作，你会期望
的方式来。这些改进都涉及betterness - 的
编译器决定哪些两个重载的是对于给定的
论点更好的方式

There are a number of small improvements to overload resolution, which will likely result in more things just working the way you’d expect them to. The improvements all relate to "betterness" – the way the compiler decides which of two overloads is better for a given argument.

于是我问：

问

究竟如何是的改进重载的进场在C＃6？而如何的是从不同的C＃5的（例？文档？）的

How exactly is the Improved overload resolution comes into play in C#6? And how it is different from C#5 (Example? Documentation?)

推荐答案

我相信在这里的意思是好betterness规则，是的在罗斯林GitHub库记录

I believe what is meant here is the "better betterness" rules which are documented in the Roslyn github repo.

示例代码：

using System;

class Test
{
    static void Foo(Action action) {}
    static void Foo(Func<int> func) {}
    static int Bar() { return 1; }

    static void Main()
    {
        Foo(Bar);        
    }
}

在<$ c使用C＃5编译器（例如： $ C> C：\Windows\Microsoft.NET\Framework\v4.0.30319\ ）这给了两个错误：

test.cs中（11,9）：错误CS0121：呼叫是以下方法或属性之间暧昧：结果
&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;测试包含.foo（System.Action）'和'Test.Foo（System.Func）'结果
test.cs中（11,13）：错误CS0407：'诠释Test.Bar（）'有错误的返回类型

Test.cs(11,9): error CS0121: The call is ambiguous between the following methods or properties:
     'Test.Foo(System.Action)' and 'Test.Foo(System.Func)'
Test.cs(11,13): error CS0407: 'int Test.Bar()' has the wrong return type

使用C＃6编译器，它编译罚款。

Using the C# 6 compiler, it compiles fine.

同样使用lambda表达式精确匹配，这会产生与C＃5编译暧昧过载错误，但不能用于C＃6：

Likewise using exact matching for lambda expressions, this generates an ambiguous overload error with the C# 5 compiler, but not for C# 6:

using System;

class Test
{
    static void Foo(Func<Func<long>> func) {}
    static void Foo(Func<Func<int>> func) {}

    static void Main()
    {
        Foo(() => () => 7);
    }
}

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