为什么C＃6.0不允许在使用Null传播运算符时设置非空可空结构的属性？ [英] Why C# 6.0 doesn't let to set properties of a non-null nullable struct when using Null propagation operator?

问题描述

假设我们有以下代码：

struct Article
{
    public string Prop1 { get; set; }
}

Article? art = new Article();
art?.Prop1 = "Hi"; // compile-error

编译错误是

CS0131作业的左侧必须是变数，属性或索引。

CS0131 The left-hand side of an assignment must be a variable, property or indexer.

实际上 art？.Prop1 是一个属性，应该被认为是有效的赋值！

我没有看到任何问题，代码无效。

Actually art?.Prop1 is a property and should be considered as a valid assignment!
I don't see any problem with assignment to make this code invalid.

为什么C＃6.0不允许设置一个非空的可空结构的属性？

或者，一行代码的任何建议使分配有效将不胜感激。

Why C# 6.0 doesn't let to set properties of a non-null nullable struct ?
Alternately any suggestion for one line code to make assignment valid would be appreciated.

推荐答案

此代码：

Article? art

将定义 Nullable< Article> 但后来当你这样做：

will define a Nullable<Article> but later when you do:

art?.Prop1 = "Hi";

这意味着使用Null传播/条件运算符。

This will mean using Null propagation/conditional operator.

空传播/条件运算符用于访问属性，而不是设置它们。因此你不能使用它。

Null propagation/conditional operator is for accessing properties, not setting them. Hence you can't use it.

由于@Servy在注释中说，Null条件运算符的结果总是一个值，您不能为值分配值，因此错误。

As @Servy said in the comments, the result of Null conditional operator is always a value and you can't assign a value to a value, hence the error.

如果你只是想设置属性，那么你不需要？ code> 与 Nullable< T> 类型在声明时使用，这是语法糖：

If you are only trying to set the property then you don't need ? with the object name, ? with Nullable<T> types is used at the time of declaration, which is syntactic sugar to:

Nullable<Article> art; //same as Article? art

这篇关于为什么C＃6.0不允许在使用Null传播运算符时设置非空可空结构的属性？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！