三元/空合并运算符和赋值表达式的右边？ [英] Ternary/null coalescing operator and assignment expression on the right-hand side?

问题描述

虽然三元和空COALESCE运营商在C＃中，我发现，它有可能在表达式的右边使用分配，例如，这是一个有效的C＃代码尝试：

While experimenting with ternary and null coalesce operators in C# I discovered that it is possible to use assignments on the right-hand side of expressions, for example this is a valid C# code:

int? a = null;
int? b = null;
int? c = a ?? (b = 12);
int? d = a == 12 ? a : (b = 15);

奇怪的是，不仅在表达的右手侧的分配评价，以它自己的右手边（即这里的第三行进行评估，以 12 ，而不是像 b = 12 =>无效），但这种分配也有效地发挥作用，从而使两个变量在一个语句分配。你也可以使用任何可计算的表达对这项任务的右边，与任何可用的变量。

Strangely enough, not only the assignment on the right-hand side of the expression is evaluated to its own right-hand side (meaning that the third line here is evaluated to 12 and not to something like b = 12 => void), but this assignment also effectively works, so that two variables are assigned in one statement. One can also use any computable expression on the right-hand side of this assignment, with any available variable.

这行为在我看来是很奇怪的。我记得和的麻烦，如果（A = 2）而不是如果（A == 2）用C 比较++，它总是评估为真正这是从基本/哈斯克尔切换到C ++后，一个常见的错误。

This behaviour seems to me to be very strange. I remember having troubles with if (a = 2) instead of if (a == 2) comparison in C++, which is always evaluated to true and this is a common mistake after switching from Basic/Haskell to C++.

时它记录的功能？是否有任何名字？

Is it a documented feature? Is there any name for it?

推荐答案

这恰好为的赋值运算符也将在返回值：

This happens as consequence of the assignment operator also returning the value:

赋值运算符（=）存储在存储位置，属性或索引其左侧操作数表示其右边的操作数的值，并返回值作为其结果。

The assignment operator (=) stores the value of its right-hand operand in the storage location, property, or indexer denoted by its left-hand operand and returns the value as its result.

表达式 B = 12 不仅分配12 b ，也将返回该值。

The expression b = 12 not only assigns 12 to b, but also returns this value.

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