unboxing

boxing and unboxing, why aren't the outputs both “System.Object”?

由 倖福魔咒の 提交于 2020-12-01 10:08:04
问题 I got the following code: object var3 = 3; Console.WriteLine(var3.GetType().ToString()); Console.WriteLine(typeof(object).ToString()); The output is: System.Int32 System.Object Why aren't they both System.Object ? 回答1: If you're asking why the boxedObject.GetType() does not return Object.. check out the image under the Section 'Boxing Conversion' on the MSDN Boxing and Unboxing page. Good question btw.. atleast my understanding of your question. Although I may not be technically correct, it

boxing and unboxing, why aren't the outputs both “System.Object”?

由 久未见 提交于 2020-12-01 10:07:02
问题 I got the following code: object var3 = 3; Console.WriteLine(var3.GetType().ToString()); Console.WriteLine(typeof(object).ToString()); The output is: System.Int32 System.Object Why aren't they both System.Object ? 回答1: If you're asking why the boxedObject.GetType() does not return Object.. check out the image under the Section 'Boxing Conversion' on the MSDN Boxing and Unboxing page. Good question btw.. atleast my understanding of your question. Although I may not be technically correct, it

How to modify the boxed value without creating a new object in C#?

由 那年仲夏 提交于 2020-05-24 05:05:21
问题 How to modify the boxed value without creating a new object in C#? E.g. if I have object o = 5; and I want to change the value of the boxed 5 to 6 , how can I do that? The o = 6; will create a new object on the heap and assign the reference to that object to the o . Are there any other ways to change the boxed value? 回答1: You can do the "boxing" yourself, than you can modify it. class Box { public int Value { get;set;} } This prevents the automatic boxing. If you define yourself an conversion

装箱（boxing）和拆箱（unboxing） [转]

由 我是研究僧i 提交于 2020-03-01 14:06:30
1. 装箱和拆箱 装箱 就是把“值类型”转换成“引用类型”； 拆箱 就是把“引用类型”转换成“值类型”； 首先，我们要弄明白为什么需要装箱和拆箱。C#的所有类型，包括int、boo等，都继承自System.Object，但是却又有值类型和引用类型之分。这时你要问，int是继承自object类型的，object是引用类型，那为何int不是引用类型而是值类型的呢？这就涉及到装箱和拆箱的概念了。 我们知道对象是创建在堆上的，它的创建和销毁必然带来额外的CPU和内存消耗。如果将int，boo等微小而常用的数据类型都放在堆上创建和销毁，语言的性能将会被极大的限制，有时甚至是无法忍受的。C#将值类型和引用类型分开，值类型直接在栈中被创建，超过作用域后直接销毁。当需要值类型成为对象时，使用装箱操作，让值类型变为一个引用类型的对象。这样，我们就可以使用object作为通用的接口统一语言内的一切类型。 拆箱 在MSDN官方文档里用的是 取消装箱。 事实上拆箱是装箱的逆操作，也就是说我们只对装过箱的引用类型（通常是object对象）进行拆箱操作。单纯拆箱操作的后果无法设想的。 装箱和拆箱是C#的核心概念，C#利用其完成类型系统的统一。有了装箱，任何类型的值都可以视为一个对象。CLR在装箱时是将值类型包装到System.Object的内部，再将其存储到托管堆上。拆箱是从对象中提取值类型

creating custom instance of UArray

由 落爺英雄遲暮 提交于 2020-01-10 03:59:09
问题 Suppose I have a simple data type like: data Cell = Open | Blocked and I'd like to use a UArray Int Cell . Is there an easy way to do this? Can I somehow reuse the definition for UArray Int Bool ? 回答1: This answer explains why Vectors are better than Arrays, so I'm going to give you the answer for unboxed vectors. I did try deriving an MArray and IArray instance for Cell based on the Bool instances, but the Bool instances are quite complicated; it would be at least as ugly as manually

Does unboxing occur when a class's value-type member is referenced?

由 元气小坏坏 提交于 2020-01-01 05:22:09
问题 I read What is boxing and unboxing and what are the trade offs? but can't understand one thing. Suppose I have a class: class MyClass { public int Value { get; set; } } And I want to get value within my method: void MyFunc(MyClass cls) { int i = cls.Value; } As a class placed in heap, I guess that Value placed in a heap too? And therefore operation int i = cls.Value; is unboxing? Or it's not unboxing? 回答1: Stop thinking about stack and heap ; that's completely the wrong way to think about it.

Integer auto-unboxing and auto-boxing gives performance issues?

由 て烟熏妆下的殇ゞ 提交于 2019-12-30 17:23:30
问题 We are currently doing some iterations and other operations using x++; where x is an Integer and not an int . Operations may be repeated throughout some user operations on our system but nothing too complex or numerous like a Mathematical application, maximum up to 10000 times per user transaction.. Will this unboxing and later boxing affect our performance by some noticeable milliseconds ? 回答1: http://download.oracle.com/javase/1.5.0/docs/guide/language/autoboxing.html "The performance of

Integer auto-unboxing and auto-boxing gives performance issues?

由 拈花ヽ惹草 提交于 2019-12-30 17:22:52
问题 We are currently doing some iterations and other operations using x++; where x is an Integer and not an int . Operations may be repeated throughout some user operations on our system but nothing too complex or numerous like a Mathematical application, maximum up to 10000 times per user transaction.. Will this unboxing and later boxing affect our performance by some noticeable milliseconds ? 回答1: http://download.oracle.com/javase/1.5.0/docs/guide/language/autoboxing.html "The performance of

Inconsistent null equality check scala 2.11.7

由 旧时模样 提交于 2019-12-23 16:28:00
问题 Edit: This issue no longer exists in Scala 2.12.6 Original question (for Scala 2.11.7): Why so strange warning? scala> null.asInstanceOf[Double] res0: Double = 0.0 scala> null.asInstanceOf[Double] == null <console>:11: warning: comparing values of types Double and Null using `==' will always yield !!!!false!!!! null.asInstanceOf[Double] == null ^ res1: Boolean = true //!!!! scala> 0.0 == null <console>:11: warning: comparing values of types Double and Null using `==' will always yield false 0

Unboxing a null boxed object throws unexpected NullPointerException

由 故事扮演 提交于 2019-12-21 17:13:26
问题 If you run the following code, public class Foo{ public static void main(String[] args){ int id = new Bar().getId(); // throws unexpected NullPointerException } private static class Bar{ private final Integer id; public Bar(){ this(null); } public Bar(Integer id){ this.id = id; } public Integer getId(){ return id; } } } you will get the following stacktrace, Exception in thread "main" java.lang.NullPointerException at Foo.main(Foo.java:3) How come there's no compiler warning or anything? IMHO
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