immutability

问题 I was looking for a built-in attribute to specify that a type is immutable, and I found only System.ComponentModel.ImmutableObjectAttribute. Using Reflector, I checked where it was used, and it seems that the only public class that uses it is System.Drawing.Image... WTF? It could have been used on string, int or any of the primitive types, but Image is definitely not immutable, there are plenty of ways to alter its internal state (using a Graphics or the Bitmap.SetPixel method for instance).

问题 Is it true that if I only use immutable data type, my Java program would be thread safe? Any other factors will affect the thread safety? ****Would appreciate if can provide an example. Thanks!** ** 回答1: Thread safety is about protecting shared data and immutable objects are protected as they are read only. Well apart from when you create them but creating a object is thread safe. It's worth saying that designing a large application that ONLY uses immutable objects to achieve thread safety

问题 I am trying to dynamically get nearby markers from the server and print on a map without success. When I update map location I am getting below warnings. The expected behaviour is getting markers printed on the map when I drag map but instead it doesn't show any dynamic fetched markers but show warnings. 20:27:15: [Unhandled promise rejection: TypeError: undefined is not an object (evaluating 'object[key]')] - node_modules/immutability-helper/index.js:81:44 in - node_modules/immutability

问题 This question is somewhat related to How to pass props to {this.props.children}. That may sound like a dumb question which has been answered a million times, but I can't figure it out what is true and what is not from what I've read so far. I can't find detailed information about this topic on either react or react native documentation. So, does anyone knows how props are handled (under the hood) in react native? I'm asking this because I've read in several places either one of: props are

问题 I have following code:- public class StaticImplementer { private static String str= "ABC"; public static void main(String args[]) { str = str + "XYZ"; } } Questions:- Here String str is static, then where this object will be stored in memory? Since String is immutable, where the object for "XYZ" will be stored? Where will be final object will be Stored? And how will garbage collection will be done? 回答1: Here String str is static, then where this object will be stored in memory? String str is

问题 If I create an immutable class. All the fields have to be final. If I use stringbuilder in that like this final StringBuilder s = new StringBuilder("Hello "); , then the append function can append the value of the s and the class wont be immutable. Please advice. 回答1: It's "shallow-immutable" in that you can't change the fields themselves, but it's not fully immutable - which means you lose pretty much all the benefits associated with immutability. Basically to achieve immutability, all the

问题 I am learning the C programming language and am running into difficulties in understanding the minute differences between pointers, arrays and read only memory. I am working with the following example: char *myCards = "JQK"; From what I understand what this line of code accomplishes is it creates a null terminated string of characters in a read only section of memory that is accessible via the char pointer myCards . This means that I am able to compile the following but would receive an error

问题 I have an immutable object, which is capsulated in class and is global state. Lets say i have 2 threads that get this state, execute myMethod(state) with it. And lets say thread1 finish first. It modify the global state calling GlobalStateCache.updateState(state, newArgs); GlobalStateCache { MyImmutableState state = MyImmutableState.newInstance(null, null); public void updateState(State currentState, Args newArgs){ state = MyImmutableState.newInstance(currentState, newArgs); } } So thread1

问题 if I want to express something like [just a simple example]: int a = 0; for (int x = 0; x < n; x += 1) a = 1 - a; what should I do in Haskell, since it doesn't have variable concept? (maybe wrong, see: Does Haskell have variables?) 回答1: Often, repetition that you would perform with a loop in a procedural language is accomplished with recursion in Haskell. In this case, you should think about what the result of the loop is. It appears to alternate between 0 and 1. There are several ways to do

问题 React suggests not to mutate props. I was operating under the impression that when props are passed in, they would be immutable or frozen. The code below does not throw any errors and mutates the prop. Is this a bug? try{ var a = this.props.a; a.push('one') a.push('two') a.push('three') console.log(a) }catch(err){ console.log(err) } 回答1: I'm not sure of the exact reasoning behind it or if that's documented somewhere but I could take a guess: Freezing any assignment to a variable is not easy