shallow-copy

问题 Consider the following procedure taken from SICP: (define (make-withdraw balance) (lambda (amount) (if (>= balance amount) (begin (set! balance (- balance amount)) balance) "Insufficient funds"))) Suppose I say: (define x (make-withdraw 100)) make-withdraw returns a procedure ( (lambda (amount) ... ) ) inside a new environment called e2 (enclosing the binding for the variable balance ), and binds that procedure to x in the global frame. Now, say I call: (f x) where (define (f y) (y 25)) 1 . I

问题 In python, if I have x = y any modification to x will also modify y, and I can do x = deepcopy(y) if I want to avoid modifying y while working on x Say, instead, that I have: myFunc(): return y def main(): x = myFunc() Is it still the case that modifying x will modify y, or since it is a return from another function it will be like a deepcopy? 回答1: It will be a shallow copy, as nothing has been explicitly copied. def foo(list): list[1] = 5 return list For example: >>> listOne = [1, 2] >>>

问题 How is Deep copy being done in python for lists? I am a little confused for copying of lists. Is it using shallow copy or deep copy? Also, what is the syntax for sublists? is it g=a[:] ? 回答1: The new list is a copy of references. g[0] and a[0] both reference the same object. Thus this is a shallow copy. You can see the copy module's deepcopy method for recursively copying containers, but this isn't a common operation in my experience. Stylistically, I prefer the more explicit g = list(a) to

问题 I read in an SO topic an answer from Matt Dowle about a shallow function to make shallow copies in data.table . However, I can't find the topic again. data.table does not have any exported function called shallow . There is an internal one but not documented. Can I use it safely? What is its behavior? What I would like to do is a memory efficient copy of a big table. Let DT be a big table with n columns and f a function which memory efficiently adds a column. Is something like that possible?

问题 This should be a pretty basic question, but I've been having a little trouble finding a definite answer. When you have an array of values and you use the .ToArray() method does it create a deep or shallow copy of the array? 回答1: No. You can easily verify this by writing a small program to test. 来源： https://stackoverflow.com/questions/10387415/in-c-sharp-does-array-toarray-perform-a-deep-copy

问题 I have the following problem: I have a class which should do this: Obj o; Obj o1(o), o1=o; // deep-copies const Obj c(o), c=o; // deep-copies const Obj c1(c), c1=c; // shallow-copies Obj o2(c), o2=c; // deep-copies How can I do this preferably without inheritance? (I mean I would do Const_obj inheriting from Obj otherwise.) EDIT: Using o.clone() directly is not an option because then I could easily introduce bugs by accidentally not cloning. EDIT: Finally, there is a proper, complete solution

问题 Although I know the main difference between Deep Copy and Shallow Copy but what I want to ask here is something practical. I have NSArray *firstArray = [NSArray arrayWithObjects:@"first", @"second",@"third", nil]; NSArray *secondArray = firstArray; secondArray = nil; NSLog(@"First Array : %@",firstArray); NSLog(@"Secon Array : %@",secondArray); Both the firstArray and secondArray has the same reference as seen by putting break point. Now my question is this, if both have same REFERENCE then

问题 I want to implement a simple VersionedModel base model class for my app engine app. I'm looking for a pattern that does not involve explicitly choosing fields to copy. I am trying out something like this, but it is to hacky for my taste and did not test it in the production environment yet. class VersionedModel(BaseModel): is_history_copy = db.BooleanProperty(default=False) version = db.IntegerProperty() created = db.DateTimeProperty(auto_now_add=True) edited = db.DateTimeProperty() user = db

问题 I need to add a UIElement to two different canvases, but one UIElement can only be a child of ONE canvas, so I have to create a ShallowCopy (DeepCopy not needed) of the UIElement . I want to use MemberwiseClone , but it's protected, I cannot use it. I also want to define an extension method UIElement.ShallowCopy , but it sill still call MemberwiseClone , which is protected again. EDIT: Tried all the following, but all of them failed in Silverlight environment: // System.Runtime.Serialization

问题 Suppose I have the following class: public class Author { public int ID {get; private set;} public string firstName {get; private set;} public string lastName {get; private set; } public Author(int id, string firstname, string lastname) { this.ID = ID; this.firstName = firstname; this.lastName = lastName; } public static Author Clone(Author clone) { Author copyAuth = new Author(clone.ID, clone.firstName, clone.lastName); return copyAuth; } } and public class Book { public string bookTitle