mutable

问题 Why would the map method mutate the original array when its initial purpose is to create a new array ? I have an array of object which I pass to a pure function which in turn maps the given array and return a new one. Then I notice that the original array was also changed.. I understand the concept that Object in Js are passed by reference and all but still cant quite grab why would the implementation of map would mutate the original array, kinda beats the purpose IMO. var initialArray = [ {

问题 why or for what reason is it not possible to declare a class member variable in C++ as static mutable ? Something like static mutable int t; //This won't compile For me, there is no reason to ban such declarations. E.g. for reasons like maintaining a global class-wide statistics, it may be convenient to have static variable that can be altered by (logically) const methods. So either this is sort of a misdesign in C++ and unnecessarily complicated, or there is a practical or theoretical reason

问题 I have a struct: pub struct CommunityContents { pub friends: RefCell<HashMap<FriendID, FriendData>>, pub index: RefCell<HashMap<u64, BTreeMap<FriendID, FriendData>>>, pub authenticated: bool, pub age: u64, pub height: u64, } Which is protected with a RwLock with a parent struct: pub struct Community { pub community_contents: RwLock<CommunityContents>, } pub struct FriendData { pointer: Rc<Data>, } pub struct Data { pub key: Key, pub friend_ids: Vec<FriendID>, } I want to be able to modify the

问题 In Python, we can use the @property decorator to manage access to attributes. For example, if we define the class: class C: def __init__(self,value): self._x = value @property def x(self): """I'm the 'x' property.""" return self._x we can get the value of x, but not change it: c = C(1) #c.x = 4 # <= this would raise an AttributeError: can't set attribute However, if the attribute is of a mutable type (e.g., a list), we can set a different value for a position of the attribute: c = C([0,0]) c

问题 A: Bitmap immutableBmp= BitmapFactory.decodeResource(getApplicationContext().getResources(),R.drawable.sample); mutableBitmap=immutableBmp.copy(Bitmap.Config.ARGB_8888, true); B: Bitmap immutableBmp= BitmapFactory.decodeFile(filePath); mutableBitmap=immutableBmp.copy(Bitmap.Config.ARGB_8888, true); C: BitmapFactory.Options options = new BitmapFactory.Options(); options.inMutable=true; myBitmap=BitmapFactory.decodeFile(filePath,options); A works but B and C don't. I am trying to convert an

问题 A: Bitmap immutableBmp= BitmapFactory.decodeResource(getApplicationContext().getResources(),R.drawable.sample); mutableBitmap=immutableBmp.copy(Bitmap.Config.ARGB_8888, true); B: Bitmap immutableBmp= BitmapFactory.decodeFile(filePath); mutableBitmap=immutableBmp.copy(Bitmap.Config.ARGB_8888, true); C: BitmapFactory.Options options = new BitmapFactory.Options(); options.inMutable=true; myBitmap=BitmapFactory.decodeFile(filePath,options); A works but B and C don't. I am trying to convert an

问题 I have a class that is compared only based on the content of its attributes, so that two objects with the same values are equivalent. class a(object): def __init__(self, value): self.value = value def __repr__(self): return 'a(value={})'.format(self.value) def __hash__(self): return hash(self.__repr__()) def __eq__(self, other): if not isinstance(other, self.__class__): return NotImplemented return self.value == other.value def __ne__(self, other): return not self.__eq__(other) When I create

问题 I am trying to use Python term to explain why the following happens, can somebody explain why tmp becomes to [[1,2,3]] not stay as [[1,2]] ? arr = [] tmp = [1,2] arr.append(tmp) print arr # [[1,2]] tmp.append(3) print arr # [[1,2,3]] 回答1: arr = [] is an empty list, and when you append tmp to it via: tmp = [1, 2] arr.append(tmp) You are putting tmp in the arr list, thus giving you arr = [tmp] which can be expanded to arr = [[1,2]] . But the neat thing here is that you maintain a reference to

问题 I am trying to use Python term to explain why the following happens, can somebody explain why tmp becomes to [[1,2,3]] not stay as [[1,2]] ? arr = [] tmp = [1,2] arr.append(tmp) print arr # [[1,2]] tmp.append(3) print arr # [[1,2,3]] 回答1: arr = [] is an empty list, and when you append tmp to it via: tmp = [1, 2] arr.append(tmp) You are putting tmp in the arr list, thus giving you arr = [tmp] which can be expanded to arr = [[1,2]] . But the neat thing here is that you maintain a reference to

问题 please dont marked as duplicate , as the question is slightly different ---> null cannot be cast to non-null type kotlin.collections. MutableList Scenerios :- i have been performing delete cart using retrofit.. if atleast one item is present ,it displays in recyclerview 2.if cart is empty ,it crashes with a above error here is my adapter code:- class CartAdapter(context: Context, dataList: MutableList<DataCart?>) : RecyclerSwipeAdapter<CartAdapter.CustomViewHolder>() { //added