C#中的结构真的不能为空吗? [英] Can structs really not be null in C#?
本文介绍了C#中的结构真的不能为空吗?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
下面是一些代码,演示了我无法将结构类型声明和初始化为 null.Nullable 类型是一个结构体,为什么我可以设置它为空?
Below is some code that demonstrates I cannot declare and initialize a struct type as null. The Nullable type is a struct, so why am I able to set it to null?
Nullable<bool> b = null;
if (b.HasValue)
{
Console.WriteLine("HasValue == true");
}
//Does not compile...
Foo f = null;
if (f.HasValue)
{
Console.WriteLine("HasValue == true");
}
其中 Foo
定义为
public struct Foo
{
private bool _hasValue;
private string _value;
public Foo(string value)
{
_hasValue = true;
_value = value;
}
public bool HasValue
{
get { return _hasValue; }
}
public string Value
{
get { return _value; }
}
}
问题已得到解答(见下文).为了澄清,我将发布一个示例.C# 代码:
The question has been answered (see below). To clarify I'll post an example. The C# code:
using System;
class Program
{
static void Main(string[] args)
{
Nullable<bool> a;
Nullable<bool> b = null;
}
}
产生以下IL:
.method private hidebysig static void Main(string[] args) cil managed
{
.entrypoint
// Code size 10 (0xa)
.maxstack 1
.locals init ([0] valuetype [mscorlib]System.Nullable`1<bool> a,
[1] valuetype [mscorlib]System.Nullable`1<bool> b)
IL_0000: nop
IL_0001: ldloca.s b
IL_0003: initobj valuetype [mscorlib]System.Nullable`1<bool>
IL_0009: ret
} // end of method Program::Main
a 和 b 被声明,但只有 b 被初始化.
a and b are declared, but only b is initialized.
推荐答案
C# 编译器为您提供了一些糖,因此您确实在这样做:
The C# compiler provides you with a bit of sugar so you really are doing this:
Nullable<bool> b = new Nullable<bool>();
这里是语法糖
bool? b = null;
if (b ?? false)
{
b = true;
}
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