immutability

问题 From a recent SO question (see Create a dictionary in python which is indexed by lists) I realized I probably had a wrong conception of the meaning of hashable and immutable objects in python. What does hashable mean in practice? What is the relation between hashable and immmutable? Are there mutable objects that are hashable or immutable objects that are not hashable? 回答1: Hashing is the process of converting some large amount of data into a much smaller amount (typically a single integer)

问题 I have a request object that comes from werkzeug. I want to change a value on this request object. This is not possible because werkzeug request objects are immutable. I understand this design decision, but I need to change a value. How do I do this? >>> request <Request 'http://localhost:5000/new' [POST]> >>> request.method 'POST' >>> request.method = 'GET' *** AttributeError: read only property I tried doing a deepcopy , but the resulting copy is immutable also. I guess I could just create

问题 All is it possible to get true/false flag for class having mutable field? Could I distinguish during compilation between struct A { private: mutable int _x; }; and struct B { private: int _x; }; More complex question, is it possible to do so NOT knowing name of the field? 来源： https://stackoverflow.com/questions/35519596/c-compile-time-check-if-type-has-mutable-fields

问题 While reading akka docs right under messages and immutability section, It mentions about "explicitly exposing the state" inside case class. So my questions are; What is meant by saying "explicitly exposing the state" for case class? In order to achieve immutability, isn't it enough to write "case" for a class? Or I should be careful about its usage ? 回答1: What is meant by saying "explicitly exposing the state" for case class? The actor below represents its state with a mutable Set[Int] ,

问题 This question is an extension of this question. I have a class similar to the following. class HighlightableStructure { private final HighlightableStructure NEXT; HighlightableStructure(HighlightableStructure next) { NEXT = next; } } where a HighlightableStructure points to the next structure to highlight. Sometimes, these HighlightableStructure s loop around and refer to a previous HighlightableStructure , but not the first in the chain. Something like h_1 -> h_2 ->h_3 -> ... -> h_n -> h_2,

问题 When I executed the following steps, both tuples ( a and b ) haven't retained their original IDs even when I reassigned older values ( (1,2) ). >>> a , b = (1,2) , (1,2) >>> a (1, 2) >>> b (1, 2) >>> id(a) , id(b) (80131912, 91541064) >>> a , b = (3,4) , (3,4) >>> a (3, 4) >>> b (3, 4) >>> id(a) , id(b) (91559048, 91689032) >>> a , b = (1,2) , (1,2) >>> a (1, 2) >>> b (1, 2) >>> id(a) , id(b) (91556616, 91550408) But in the following case, both have gotten their older IDs back. >>> a = (1,2)

问题 I have this map that looks like this: val fields: Map[(Int, Int), Field] and I thought about doing something like: val fields: Map[(Int, Int), Field] = Map( for(a <- 0 to 10) { (0, a) -> new Field(this, 0, a) } ) instead of a long copy/paste list like: (0, 0) -> new Field(this, 0, 0), (1, 0) -> new Field(this, 1, 0), (2, 0) -> new Field(this, 2, 0), (3, 0) -> new Field(this, 3, 0), (4, 0) -> new Field(this, 4, 0), (5, 0) -> new Field(this, 5, 0), (6, 0) -> new Field(this, 6, 0), (7, 0) -> new

问题 Parent component is a header Child component is a form which is used to change values appearing in the header after a save which fires a redux action. I set the child state with constructor(props) { super(props); this.state = { object: { ...props.object }, hidden: props.hidden, }; } The form is used to render the state.object and modify the state.object. When I modify state.object, the props from the parent component change as well. handleObjectChange = (event, key, subkey) => { console.log(

问题 It is considered a good practice to avoid using mutable variables in Scala. From "Programming in Scala, 2nd Edition", page 52: "Scala allows you to program in an imperative style, but encourages you to adopt a more functional style" and later "Scala encourages you to lean towards vals, but ultimately reach for the best tool given the job at hand." How do you make this imperative construct elegant in Scala (focusing on variable count ): var count = 0 val foo = getRequest() if(foo.isJsonObject)

问题 I am trying to implement In App Purchases, and I am tracking which purchases a user has purchased via NSUserDefaults . I have a function that sets the values of each purchase, but when it runs, I get an error saying that I am mutating the dictionary of purchase values even though the dictionary is declared with a var instead of a let and is an NSMutableDictionary . Sometimes it does work, but most of the time it doesn't. I get a few warnings about declaring my variables with let instead of