C#6 改进的重载解析 - 说明？

Question

在 C#6 的所有新特性中，（对我来说）最神秘的特性是 "improved overload resolution".

可能是因为我 couldn't find 与 info/examples/explanation 有关。

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

正在查看 roslyn wiki

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.

所以我问：

问题:

改进的重载解析 究竟如何在 C#6 中发挥作用？它与 C#5 有何不同（示例？文档？）

Answer 1

我相信这里的意思是 "better betterness" 规则，即 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);        
    }
}

使用 C# 5 编译器（例如在 c:\Windows\Microsoft.NET\Framework\v4.0.30319\ 中）会产生两个错误：

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，可以正常编译。

同样对 lambda 表达式使用精确匹配，这会在 C# 5 编译器中产生不明确的重载错误，但在 C# 6 中不会：

using System;

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

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

C#6 改进的重载解析 - 说明？

C#6's Improved overload resolution - clarification?

c#

c#-6.0