immutability

问题 I am stuck with using immutable objects with collections. Let assume I have the following class : //in .h class Data { public: Data(const DataObj& data); Data(const Data&); const DataObj& getDataObj() const; private: const DataObj _data; //actually several objects or simple type } inline const DataObj& Data::getDataObj() const {return _data}; //in .c Data(const DataObj& data) : _data(data){}; Data(const Data& original) : _data(original._data){} The issue is that when I want to use collections

问题 Calling expert Scala developers! Let's say you have a large object representing a writable data store. Are you comfortable with this common Java-like approach: val complexModel = new ComplexModel() complexModel.modify() complexModel.access(...) Or do you prefer: val newComplexModel = complexModel.withADifference newComplexModel.access(...) If you prefer that, and you have a client accessing the model, how is the client going to know to point to newComplexModel rather than complexModel? From

问题 It certainly does not break from the standard practice of the .NET framework. When I see a a + b I always assume something new will be created. static void Main(string[] args) { var list = BuildList(ImmutableList<int>.Empty); var sum = (list + 500).Sum(); Console.WriteLine(sum); Console.ReadLine(); } static ImmutableList<int> BuildList(ImmutableList<int> list) { if (list.Count < 1000) { return BuildList(list + list.Count); } return list; } Update See Jon Skeet's post on what to name methods

问题 Is it possible to serialize/deserialize types with protobuf-net on Windows Phone 7/8? I've tried the code below, it seems Constructor skipping isn't supported (i.e. UseConstructor = false) so I created a parameterless constructor but the deserialization fails with "Attempt to access the method failed: Wp7Tests.ImmutablePoint.set_X(System.Double)" public class ImmutablePoint { public double X { get; private set; } public double Y { get; private set; } public ImmutablePoint() {} public

问题 This question already has answers here : variable that can't be modified (9 answers) Closed 2 years ago . In Scala I can write (and it will mean exactly the same thing it means in C#) var v = 1; v = 2; but can't write (well, of course I can write but can't compile actually though the syntax is correct) val v = 1; v = 2; Semicolons are not necessary but can be voluntarily used in Scala so I've decided to include them to let the code correspond C# more closely. val means an immutable value, a

问题 It seems that I cannot mutate anything if there is any immutable reference in my chain of dereferencing. A sample: fn main() { let mut x = 42; let y: &mut i32 = &mut x; // first layer let z: &&mut i32 = &y; // second layer **z = 100; // Attempt to change `x`, gives compiler error. println!("Value is: {}", z); } I'm getting the compiler error: error[E0594]: cannot assign to `**z` which is behind a `&` reference --> src/main.rs:5:5 | 4 | let z: &&mut i32 = &y; // second layer | -- help:

问题 In Scala, if I'm planning on having a mutable attribute (e.g. a bag of numbers) of an object, when is it appropriate to Create a var and use an immutable data structure? Create a val and use a mutable data structure? I'm going to throw a guess out that you'd want to use #2 for threaded applications? Are some of the collections thread-safe? How about in general? (Or does it not really matter?) 回答1: Between your choices 1 and 2, it doesn't matter - mutable is mutable, and if you read or modify

问题 I think this question might already have an answer here on SO, but I can't seem to find it. Please mark it as duplicate if you find an answer. I am not asking why, but how can I not let this happen? I want j to have a diffrent id than i . Say when i do, >>> i = 6 >>> j = 6 >>> id(i) 10919584 >>> id(j) 10919584 #I don't want this, I want j to point to a different object So, I get what happens in the code above(Or at least I think I do), but my question is how can I prevent it? I am asking it

问题 In discussion of this answer we realized that tuples do not have a __reversed__ method. My guess was that creating the iterator would require mutating the tuple. And yet tuples play fine with reversed . Why can't the approach used for reversed be made to work for __reversed__ as well? >>> foo = range(3) >>> foo [0, 1, 2] >>> list(foo.__reversed__()) [2, 1, 0] >>> foo [0, 1, 2] >>> bar = (0, 1, 2) >>> list(bar.__reversed__()) Traceback (most recent call last): File "<stdin>", line 1, in

问题 I'm trying to make a list which is used throughout the application immutable. I thought wrapping this list in a tuple would do the trick, but it seems that tuple(list) doesn't actually wrap, but copies the list elements. >>> a = [1, 2, 3, 4] >>> b = tuple(a) >>> b (1, 2, 3, 4) >>> a[0] = 2 >>> b # was hoping b[0] to be 2 (1, 2, 3, 4) Is there an easy way of creating a list-backed "view" on this list that is immutable (wrt. operations on this view), but reflects any change that happened to the