条件运算符感到困惑，但为什么呢?

问题描述

假设有两个类，都是同一个超类的后代，如下所示:

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

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

那么这个赋值不会通过编译器:

Then this assignment won't pass the compiler:

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

编译器抱怨 A 和 B 不兼容(无法确定条件表达式的类型，因为 'A' 和 'B' 之间没有隐式转换 [CS0173]).但它们都是 MySuperClass 类型，所以我认为这应该可行.并不是说这有什么大不了的；只需一个简单的转换就可以启发编译器.但它肯定是 C# 编译器中的一个障碍吗?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.

来自 MSDN，(?:运算符):

From MSDN, (?: Operator):

first_expression 和 second_expression 的类型必须相同，或者必须存在从一种类型到另一种类型的隐式转换.

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 和 B 不是同一类型，并且您似乎没有定义隐式转换，因此编译器会抱怨.

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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