条件运算符很困惑，但为什么？ [英] The conditional operator gets confused, but why?

问题描述

假设有两个类，同一超类的两个后代，如下：

Assume two classes, both descendants of the same superclass, like this:

class MySuperClass{}
class A : MySuperClass{}
class B : MySuperClass{}

传递编译器：

MySuperClass p = myCondition ? new A() : new B();

编译器提示A和B不兼容（无法确定条件表达式的类型因为在'A'和'B'之间没有隐式转换 [CS0173]）。但他们都是类型MySuperClass，所以在我看来这应该工作。这不是一件大事;一个简单的转换就是启发编译器所需要的。但是这肯定是C＃编译器的障碍？你不同意吗？

The compiler complains that A and B are not compatible (Type of conditional expression cannot be determined because there is no implicit conversion between 'A' and 'B' [CS0173] ). But they are both of type MySuperClass, so in my opinion this should work. Not that it's a big deal; a simple cast is all it takes to enlighten the compiler. But surely it's a snag in the C# compiler? Don't you agree?

推荐答案

条件的结果应该是相同的类型。他们不是。

The results of the conditional should be of the same type. They are not.

从 MSDN ，（？：Operator）：

From MSDN, (?: Operator):

first_expression和second_expression的类型必须相同，

Either the type of first_expression and second_expression must be the same, or an implicit conversion must exist from one type to the other.

由于 A code> B 不是相同的类型，你似乎没有定义一个隐式转换，编译器抱怨。

Since A and B are not the same type and you don't seem to have defined an implicit conversion, the compiler complains.

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