我收集了一些极端案例和脑筋急转弯，总是想听到更多。这个页面只涵盖了c#语言的一些细节，但我也发现了。net核心的东西也很有趣。例如，这里有一个没有在页面上，但我觉得不可思议:
string x = new string(new char[0]);
string y = new string(new char[0]);
Console.WriteLine(object.ReferenceEquals(x, y));
我希望输出False -毕竟，“new”(具有引用类型)总是创建一个新对象，不是吗?c#和CLI的规范都表明应该这样做。嗯，在这个特殊情况下不是这样。它输出True，并且在我测试过的框架的每个版本上都是这样。(不可否认，我还没有在Mono上尝试过……)
只是为了澄清，这只是我正在寻找的事情的一个例子-我并不是特别寻找对这个奇怪现象的讨论/解释。(这和普通的弦乐实习不一样;特别地，当调用构造函数时，字符串实习通常不会发生。)我真的是在要求类似的奇怪行为。
还有其他的宝藏吗?
当前回答
今天刚发现一件小玩意儿
public class Base
{
public virtual void Initialize(dynamic stuff) {
//...
}
}
public class Derived:Base
{
public override void Initialize(dynamic stuff) {
base.Initialize(stuff);
//...
}
}
这会引发编译错误。
对方法'Initialize'的调用需要动态分派，但不能这样做，因为它是基本访问表达式的一部分。考虑强制转换动态参数或取消基本访问。
如果我写底。初始化(stuff as object);它工作得很完美，但这似乎是一个“神奇的词”，因为它的功能完全相同，一切仍然是动态的……
其他回答
这个让我很困惑(我很抱歉篇幅太长，但它是WinForm)。我之前在新闻组里发的。
I've come across an interesting bug. I have workarounds but i'd like to know the root of the problem. I've stripped it down into a short file and hope someone might have an idea about what's going on. It's a simple program that loads a control onto a form and binds "Foo" against a combobox ("SelectedItem") for it's "Bar" property and a datetimepicker ("Value") for it's "DateTime" property. The DateTimePicker.Visible value is set to false. Once it's loaded up, select the combobox and then attempt to deselect it by selecting the checkbox. This is rendered impossible by the combobox retaining the focus, you cannot even close the form, such is it's grasp on the focus. I have found three ways of fixing this problem. a) Remove the binding to Bar (a bit obvious) b) Remove the binding to DateTime c) Make the DateTimePicker visible !?! I'm currently running Win2k. And .NET 2.00, I think 1.1 has the same problem. Code is below.
using System;
using System.Collections;
using System.Windows.Forms;
namespace WindowsApplication6
{
public class Bar
{
public Bar()
{
}
}
public class Foo
{
private Bar m_Bar = new Bar();
private DateTime m_DateTime = DateTime.Now;
public Foo()
{
}
public Bar Bar
{
get
{
return m_Bar;
}
set
{
m_Bar = value;
}
}
public DateTime DateTime
{
get
{
return m_DateTime;
}
set
{
m_DateTime = value;
}
}
}
public class TestBugControl : UserControl
{
public TestBugControl()
{
InitializeComponent();
}
public void InitializeData(IList types)
{
this.cBoxType.DataSource = types;
}
public void BindFoo(Foo foo)
{
this.cBoxType.DataBindings.Add("SelectedItem", foo, "Bar");
this.dtStart.DataBindings.Add("Value", foo, "DateTime");
}
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.IContainer components = null;
/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
protected override void Dispose(bool disposing)
{
if (disposing && (components != null))
{
components.Dispose();
}
base.Dispose(disposing);
}
#region Component Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.checkBox1 = new System.Windows.Forms.CheckBox();
this.cBoxType = new System.Windows.Forms.ComboBox();
this.dtStart = new System.Windows.Forms.DateTimePicker();
this.SuspendLayout();
//
// checkBox1
//
this.checkBox1.AutoSize = true;
this.checkBox1.Location = new System.Drawing.Point(14, 5);
this.checkBox1.Name = "checkBox1";
this.checkBox1.Size = new System.Drawing.Size(97, 20);
this.checkBox1.TabIndex = 0;
this.checkBox1.Text = "checkBox1";
this.checkBox1.UseVisualStyleBackColor = true;
//
// cBoxType
//
this.cBoxType.FormattingEnabled = true;
this.cBoxType.Location = new System.Drawing.Point(117, 3);
this.cBoxType.Name = "cBoxType";
this.cBoxType.Size = new System.Drawing.Size(165, 24);
this.cBoxType.TabIndex = 1;
//
// dtStart
//
this.dtStart.Location = new System.Drawing.Point(117, 40);
this.dtStart.Name = "dtStart";
this.dtStart.Size = new System.Drawing.Size(165, 23);
this.dtStart.TabIndex = 2;
this.dtStart.Visible = false;
//
// TestBugControl
//
this.AutoScaleDimensions = new System.Drawing.SizeF(8F, 16F);
this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
this.Controls.Add(this.dtStart);
this.Controls.Add(this.cBoxType);
this.Controls.Add(this.checkBox1);
this.Font = new System.Drawing.Font("Verdana", 9.75F,
System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point,
((byte)(0)));
this.Margin = new System.Windows.Forms.Padding(4);
this.Name = "TestBugControl";
this.Size = new System.Drawing.Size(285, 66);
this.ResumeLayout(false);
this.PerformLayout();
}
#endregion
private System.Windows.Forms.CheckBox checkBox1;
private System.Windows.Forms.ComboBox cBoxType;
private System.Windows.Forms.DateTimePicker dtStart;
}
public class Form1 : Form
{
public Form1()
{
InitializeComponent();
this.Load += new EventHandler(Form1_Load);
}
void Form1_Load(object sender, EventArgs e)
{
InitializeControl();
}
public void InitializeControl()
{
TestBugControl control = new TestBugControl();
IList list = new ArrayList();
for (int i = 0; i < 10; i++)
{
list.Add(new Bar());
}
control.InitializeData(list);
control.BindFoo(new Foo());
this.Controls.Add(control);
}
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.IContainer components = null;
/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
protected override void Dispose(bool disposing)
{
if (disposing && (components != null))
{
components.Dispose();
}
base.Dispose(disposing);
}
#region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.components = new System.ComponentModel.Container();
this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
this.Text = "Form1";
}
#endregion
}
static class Program
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
}
}
}
有趣的是，当我第一次看到它时，我认为这是c#编译器正在检查的东西，但即使你直接发出IL来消除任何干扰的机会，它仍然会发生，这意味着它真的是newobj操作代码正在进行检查。
var method = new DynamicMethod("Test", null, null);
var il = method.GetILGenerator();
il.Emit(OpCodes.Ldc_I4_0);
il.Emit(OpCodes.Newarr, typeof(char));
il.Emit(OpCodes.Newobj, typeof(string).GetConstructor(new[] { typeof(char[]) }));
il.Emit(OpCodes.Ldc_I4_0);
il.Emit(OpCodes.Newarr, typeof(char));
il.Emit(OpCodes.Newobj, typeof(string).GetConstructor(new[] { typeof(char[]) }));
il.Emit(OpCodes.Call, typeof(object).GetMethod("ReferenceEquals"));
il.Emit(OpCodes.Box, typeof(bool));
il.Emit(OpCodes.Call, typeof(Console).GetMethod("WriteLine", new[] { typeof(object) }));
il.Emit(OpCodes.Ret);
method.Invoke(null, null);
如果检查string，它也等于true。这意味着这个操作代码必须有特殊的行为来实习空字符串。
c#支持数组和列表之间的转换，只要数组不是多维的，并且类型之间有继承关系，并且类型是引用类型
object[] oArray = new string[] { "one", "two", "three" };
string[] sArray = (string[])oArray;
// Also works for IList (and IEnumerable, ICollection)
IList<string> sList = (IList<string>)oArray;
IList<object> oList = new string[] { "one", "two", "three" };
注意，这是无效的:
object[] oArray2 = new int[] { 1, 2, 3 }; // Error: Cannot implicitly convert type 'int[]' to 'object[]'
int[] iArray = (int[])oArray2; // Error: Cannot convert type 'object[]' to 'int[]'
这是我最近才发现的一个……
interface IFoo
{
string Message {get;}
}
...
IFoo obj = new IFoo("abc");
Console.WriteLine(obj.Message);
乍一看，上述做法很疯狂，但实际上是合法的。不，真的(虽然我错过了一个关键部分，但它不是任何像“添加一个称为IFoo的类”或“添加一个使用别名将IFoo指向一个类”这样的俗套)。
看看你是否能找出原因:谁说你不能实例化一个接口?
PropertyInfo.SetValue()可以将int赋值给enum，将int赋值给可空的int，将enum赋值给可空的enum，但不能将int赋值给可空的enum。
enumProperty.SetValue(obj, 1, null); //works
nullableIntProperty.SetValue(obj, 1, null); //works
nullableEnumProperty.SetValue(obj, MyEnum.Foo, null); //works
nullableEnumProperty.SetValue(obj, 1, null); // throws an exception !!!
完整描述在这里
