hashable

问题 I do not understand why Data.HashTable is using Data.Hashable , which has hashWithSalt as the (only/basic) method. This does not fit with the natural optimization of computing the hash value once, and storing it in the object (natural, because Haskell objects are immutable). If I want to use HashTables with that, then I'm forced to implement hashWithSalt . (Going 1.2.0.* to 1.2.1.*, hashable re-introduced hash as a class method, but this does not help?) The actual Table implementations don't

问题 I'm trying to fix up an old tutorial from RayWenderlich's site, no longer supported. The warning appears in three files, Chain.swift, Cookie.swift and Swap.swift from the "How to Make a Game Like Candy Crush with SpriteKit and Swift:" tutorial I'm at a loss even after exploring the available replies that appear in many places. I'm struggling to understand just what this code is doing so that I can fix it. I know it's just a warning, and I can probably ignore it, but the game is also showing X

问题 As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance. Closed 7 years ago . I want to derive a class from list , add a few instance attributes to it, and make it hashable. What is a good (fast and neat) way to

问题 I have two lists I would like to modify a particular content of the first list and send the output but when I try to modify it, am getting an error TypeError: unhashable type: 'list' . I am using python with mongodb. The two lists are data = [{"id" : ["5630baac3f32df134c18b682","564b22373f32df05fc905564"],"phone" : ["9988776655","9638527410"], "Request": "Support staff", "Date": "19-11-2015"}] test = [{"phone" : "9638527410", "id": "5630baac3f32df134c18b682"}] id = {} for info in chain(data,

问题 I have a struct in Swift that looks like this: internal struct MapKey { internal let id: String internal let values: [String:String] } extension MapKey: Equatable {} func ==(lhs: MapKey, rhs: MapKey) -> Bool { return lhs.id == rhs.id && lhs.values == rhs.values } I now have the need to use MapKey as the key in a Swift dictionary, which requires MapKey to conform to the Hashable protocol. What would a correct implementation of Hashable be for a struct like this one? extension MapKey: Hashable

问题 One way to make a numpy array hashable is setting it to read-only. This has worked for me in the past. But when I use such a numpy array in a tuple, the whole tuple is no longer hashable, which I do not understand. Here is the sample code I put together to illustrate the problem: import numpy as np npArray = np.ones((1,1)) npArray.flags.writeable = False print(npArray.flags.writeable) keySet = (0, npArray) print(keySet[1].flags.writeable) myDict = {keySet : 1} First I create a simple numpy

问题 I'm using PaypalSDK to add paypal payment methods to the app I'm developing, it's already working and when the payment is succesful I'm getting a response which I'm converting into a jsonObject but I don't know how to parse it in order to extract just the code from the response. This is the response I'm getting JSON: [AnyHashable("response"): { code = "******************* -****************-**********************"; }, AnyHashable("response_type"): authorization_code, AnyHashable("client"): {

问题 I am working through an iOS swift Tetris tutorial* and have it completed and working. But I am puzzled about one particular aspect - the Hashable protocol. The function: class Block: Hashable, Printable { [...] var hashValue: Int { return self.column ^ self.row } Rows go 0..9, and Columns 0..20. The notes says of this function "We return the exclusive-or of our row and column properties to generate a unique integer for each Block.". But my understanding is that 0^1 would be the same as 1^0,

问题 I'm following this link and trying to make a singleton class. But, taking arguments (passed while initiating a class) into account so that the same object is returned if the arguments are same. So, instead of storing class name/class reference as a dict key, I want to store passed arguments as keys in dict . But, there could be unhashable arguments also (like dict , set itself). What is the best way to store class arguments and class objects mapping? So that I can return an object

问题 The python documentation mentions that if you override __eq__ and the object is immutable, you should also override __hash__ in order for the class to be properly hashable. In practice, when I do this I often end up with code like class MyClass(object): def __init__(self, a, b): self.a = a self.b = b def __eq__(self, other): if type(other) is type(self): return (self.a == other.a) and (self.b == other.b) else: return False def __hash__(self): return hash((self.a, self.b)) This is somewhat