c# 8 switch 表达式不“智能"；足够的 [英] c# 8 switch expression not "smart" enough

问题描述

这段代码很简单，只是一个普通的开关:

This code is simple, just a normal switch:

bool? isSomething = strSomething switch
{
    "I" => true,
    "D" => false,
    _   => null,
};

但是，编译器给了我以下错误:

However, the compiler gives me the following error:

CS0037 无法将 null 转换为 'bool'，因为它是不可为 null 的值类型

CS0037 Cannot convert null to 'bool' because it is a non-nullable value type

这个变量显然是一个可以为 null 的 bool bool?，为什么 c# 编译器不能在没有我必须强制转换 null 才能让它工作的情况下弄清楚这一点:

The variable is clearly a nullable bool bool?, why can't c# compiler figure this out without me having to cast the null to get it to work:

_   => (bool?)null,

我是不是没听明白?演员不是不必要的吗?

Am I not getting this right? isn't the cast unnecessary?

推荐答案

有一个打开的 issue#2387 在 c# 语言中.这可以在 thisCandidate 中针对 c# 9 修复.

There is an opened issue #2387 for this in c# lang. Which could be fixed in this candidate for c# 9.

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