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
如果作为Rec(0)调用(不在调试器下)，该函数将做什么?
static void Rec(int i)
{
Console.WriteLine(i);
if (i < int.MaxValue)
{
Rec(i + 1);
}
}
答:
在32位JIT上，它应该导致StackOverflowException 在64位JIT上，它应该将所有数字打印为int。MaxValue
这是因为64位JIT编译器应用尾部调用优化，而32位JIT则没有。
不幸的是，我手头没有一台64位机器来验证这一点，但该方法确实满足尾部调用优化的所有条件。如果有人有的话，我很想看看这是不是真的。
其他回答
我来派对晚了一点，但我有三四五
If you poll InvokeRequired on a control that hasn't been loaded/shown, it will say false - and blow up in your face if you try to change it from another thread (the solution is to reference this.Handle in the creator of the control). Another one which tripped me up is that given an assembly with: enum MyEnum { Red, Blue, } if you calculate MyEnum.Red.ToString() in another assembly, and in between times someone has recompiled your enum to: enum MyEnum { Black, Red, Blue, } at runtime, you will get "Black". I had a shared assembly with some handy constants in. My predecessor had left a load of ugly-looking get-only properties, I thought I'd get rid of the clutter and just use public const. I was more than a little surprised when VS compiled them to their values, and not references. If you implement a new method of an interface from another assembly, but you rebuild referencing the old version of that assembly, you get a TypeLoadException (no implementation of 'NewMethod'), even though you have implemented it (see here). Dictionary<,>: "The order in which the items are returned is undefined". This is horrible, because it can bite you sometimes, but work others, and if you've just blindly assumed that Dictionary is going to play nice ("why shouldn't it? I thought, List does"), you really have to have your nose in it before you finally start to question your assumption.
下面将打印False而不是抛出溢出异常:
Console.WriteLine("{0}", yep(int.MaxValue ));
private bool yep( int val )
{
return ( 0 < val * 2);
}
如果你有扩展方法:
public static bool? ToBoolean(this string s)
{
bool result;
if (bool.TryParse(s, out result))
return result;
else
return null;
}
这段代码:
string nullStr = null;
var res = nullStr.ToBoolean();
这不会抛出异常，因为它是一个扩展方法(实际上是HelperClass.ToBoolean(null))，而不是一个实例方法。这可能会令人困惑。
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
以下是我的一些建议:
当调用实例方法而不抛出NullReferenceException时，此值可以为null 不必为枚举定义默认枚举值
首先简单一点: enum NoZero ｛ Number = 1 }
public bool ReturnsFalse()
{
//The default value is not defined!
return Enum.IsDefined(typeof (NoZero), default(NoZero));
}
下面的代码实际上可以打印真!
internal sealed class Strange
{
public void Foo()
{
Console.WriteLine(this == null);
}
}
一段简单的客户端代码将导致这样的结果 HelloDelegate(奇怪的条);
public class Program
{
[STAThread()]
public static void Main(string[] args)
{
Strange bar = null;
var hello = new DynamicMethod("ThisIsNull",
typeof(void), new[] { typeof(Strange) },
typeof(Strange).Module);
ILGenerator il = hello.GetILGenerator(256);
il.Emit(OpCodes.Ldarg_0);
var foo = typeof(Strange).GetMethod("Foo");
il.Emit(OpCodes.Call, foo);
il.Emit(OpCodes.Ret);
var print = (HelloDelegate)hello.CreateDelegate(typeof(HelloDelegate));
print(bar);
Console.ReadLine();
}
}
这在大多数语言中都是正确的，只要调用实例方法时不使用对象的状态。只有在访问对象的状态时才解除引用
