immutability

问题 This question already has answers here : Immutable dictionary in Python 3: how to make keys(), items(), and values() dictionary views immutable (2 answers) What would a “frozen dict” be? (14 answers) Closed 3 years ago . In Python, when you want to use lists as keys of some dictionary, you can turn them into tuples, which are immutable and hence are hashable. >>> a = {} >>> a[tuple(list_1)] = some_value >>> a[tuple(list_2)] = some_other_value The same happens when you want to use set objects

问题 using System.Web.Script.Serialization.JavaScriptSerializer can I deserialize into an immutable object somehow? public class Item { public Uri ImageUri { get;private set; } public string Name { get; private set; } public Uri ItemPage { get;private set; } public decimal Retail { get;private set; } public int? Stock { get; private set; } public decimal Price { get; private set; } public Item(Uri imageUri, string name, Uri itemPage, decimal retail, int? stock, decimal price) { ImageUri = imageUri

问题 using System.Web.Script.Serialization.JavaScriptSerializer can I deserialize into an immutable object somehow? public class Item { public Uri ImageUri { get;private set; } public string Name { get; private set; } public Uri ItemPage { get;private set; } public decimal Retail { get;private set; } public int? Stock { get; private set; } public decimal Price { get; private set; } public Item(Uri imageUri, string name, Uri itemPage, decimal retail, int? stock, decimal price) { ImageUri = imageUri

问题 I read the following in an article Immutable objects are particularly handy for implementing certain common idioms such as undo/redo and abortable transactions. Take undo for example. A common technique for implementing undo is to keep a stack of objects that somehow know how to run each command in reverse (the so-called "Command Pattern"). However, figuring out how to run a command in reverse can be tricky. A simpler technique is to maintain a stack of immutable objects representing the

问题 What is the benefit of making fields private while creating an immutable class? I have seen why while creating immutable class, fields are declared as private? but I didn't get understand anything from this post. Can anybody please explain me the same? 回答1: The best way to explain is with an example: public class Immutable { private final char[] state = "Hi Mom".getChars(); public char[] getState() { return state.clone(); } } Here we have a properly encapsulated, immutable class. Nothing can

问题 Is there any way of using an immutable object as a model within a view-state in Spring webflow? I know Spring webflow generally tends towards setters for this kind of thing, but I was wondering if anyone knew of a custom DataBinder or WebDataBinder that could handle binding the data using a constructor? I'm also aware there's this (SPR-1488) JIRA task against the problem, which advocated direct field access. Do people advocate this way of doing things? To me it doesn't quite feel right.

问题 I'm trying to optimise a complex query in PostgreSQL 9.1.2, which calls some functions. These functions are marked STABLE or IMMUTABLE and are called several times with the same arguments in the query. I assumed PostgreSQL would be smart enough to only call them once for each set of inputs - after all, that's the point of STABLE and IMMUTABLE, isn't it? But it appears that the functions are being called multiple times. I wrote a simple function to test this, which confirms it: CREATE OR

问题 This question already has answers here : Scala final vs val for concurrency visibility (2 answers) Closed 5 years ago . In Scala, what is the difference between val a = 1 and final val fa = 1 回答1: final members cannot be overridden, say, in a sub-class or trait. Legal: class A { val a = 1 } class B extends A { override val a = 2 } Illegal: class A { final val a = 1 } class B extends A { override val a = 2 } You'll get an error such as this: :9: error: overriding value a in class A of type Int

问题 I'm afraid that this is a very silly question, but I must be missing something. Why might one want to use String.Copy(string)? The documentation says the method Creates a new instance of String with the same value as a specified String. Since strings are immutable in .NET, I'm not sure what's the benefit of using this method, as I'd think that string copy = String.Copy(otherString); would for all practical purposes seem to yield the same result as string copy = otherString; That is, except

问题 I was watching a presentation on Java, and at one point, the lecturer said: "Mutability is OK, sharing is nice, shared mutability is devil's work." What he was referring to is the following piece of code, which he considered an "extremely bad habit": //double the even values and put that into a list. List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 1, 2, 3, 4, 5); List<Integer> doubleOfEven = new ArrayList<>(); numbers.stream() .filter(e -> e % 2 == 0) .map(e -> e * 2) .forEach(e ->