immutability

The true definition of immutability?

由 随声附和 提交于 2019-12-09 05:45:02
问题 I am wondering how immutability is defined? If the values aren't exposed as public, so can't be modified, then it's enough? Can the values be modified inside the type, not by the customer of the type? Or can one only set them inside a constructor? If so, in the cases of double initialization (using the this keyword on structs, etc) is still ok for immutable types? How can I guarantee that the type is 100% immutable? 回答1: If the values aren't exposed as public, so can't be modified, then it's

Immutable/polymorphic POJO <-> JSON serialization with Jackson

由 蓝咒 提交于 2019-12-09 05:27:48
问题 I'm trying to serialize a immutable POJO to and from JSON, using Jackson 2.1.4, without having to write a custom serializer and with as few annotations as possible. I also like to avoid having to add unnecessary getters or default constructors just to satisfy the Jackson library. I'm now stuck on the exception: JsonMappingException: No suitable constructor found for type [simple type, class Circle]: can not instantiate from JSON object (need to add/enable type information?) The code: public

Use frozenset as a pair in python

由 ￣綄美尐妖づ 提交于 2019-12-09 04:48:25
问题 I would like to make a pair of two elements. I don't care about the order of the elements, so I use frozenset . I can think of the following two methods to iterate the elements back from the frozenset. Isn't there any fancier method? Thanks in advance. pair = frozenset([element1, element2]) pair2 = list(pair) elem1 = pair2[0] elem2 = pair2[1] pair = frozenset([element1, element2]) elems = [] for elem in pair: elems.append(elem) elem1 = elems[0] elem2 = elems[1] 回答1: pair = frozenset([element1

Extending Python's builtin Str

由 纵饮孤独 提交于 2019-12-09 04:13:18
问题 I'm trying to subclass str , but having some difficulties due to its immutability. class DerivedClass(str): def __new__(cls, string): ob = super(DerivedClass, cls).__new__(cls, string) return ob def upper(self): #overridden, new functionality. Return ob of type DerivedClass. Great. caps = super(DerivedClass, self).upper() return DerivedClass(caps + '123') derived = DerivedClass('a') print derived.upper() #'A123' print type(derived.upper()) #<class '__main__.DerivedClass'> print derived.lower(

Best way to define an immutable class in Objective C

由 给你一囗甜甜゛ 提交于 2019-12-09 04:13:01
问题 I am a newbie in Objective C and I was wondering what is the best way to define an immutable class in Objective-C (like NSString for example). I want to know what are the basic rules one has to follow to make a class immutable. I think that : setters shouldn't be provided if properties are used, they should be readonly to "disable" Key Value Coding , accessInstanceVariablesDirectly must be override and return NO Did I forget something ? Thanks 回答1: The first and foremost thing you should do

React Native Map - Getting markers from the server

由 拈花ヽ惹草 提交于 2019-12-09 03:40:43
I am trying to dynamically get nearby markers from the server and print on a map without success. When I update map location I am getting below warnings. The expected behaviour is getting markers printed on the map when I drag map but instead it doesn't show any dynamic fetched markers but show warnings. 20:27:15: [Unhandled promise rejection: TypeError: undefined is not an object (evaluating 'object[key]')] - node_modules/immutability-helper/index.js:81:44 in - node_modules/immutability-helper/index.js:73:29 in update - ... 16 more stack frames from framework internals App.js (Main file)

Memoizing all methods by default

由 ⅰ亾dé卋堺 提交于 2019-12-08 17:37:53
问题 I’m writing an application that collects and displays the data from a scientific instrument. One of the pieces of data is a spectrum: essentially just a list of values, plus a dictionary with some metadata. Once the data has been collected by the application it does not change, so both the list and the metadata can be considered immutable. I’d like to use this to my advantage by heavily memoizing the functions that perform calculations on the spectrum. Here’s a toy example: class Spectrum

Immutable dictionary in Python 3: how to make keys(), items(), and values() dictionary views immutable

由 无人久伴 提交于 2019-12-08 16:23:05
问题 Short version: What's the best way to override dict.keys() and friends to keep myself from accidentally modifying my (supposedly) immutable dictionary in Python 3? In a recent question I asked about Hashing an immutable dictionary in Python. Since then I have built an immutable, hashable dictionary I'm happy with. However, I realized it has a hole: the dictionary views returned by keys() , items() , and values() still allow myself accidentally to mutate my (supposedly) immutable dictionary.

Shadowing vs. Setting value in F#

由 Deadly 提交于 2019-12-08 16:09:56
问题 I've been introduced that data, by default is immutable in F#. When we reassign value to some variable, what really happens is that it rebinds the value of variable, but setting a new value is different thing. Rebinding is called Shadowing whilst setting new value is impossible if we explicitly don't say that value of the variable is mutable. Can anybody explain me this concept in details? what's difference between shadowing (rebinding) by let var = "new_value" and Setting new value like var

How to create a map of records from a javascript raw object with Immutable.js?

由 点点圈 提交于 2019-12-08 15:59:38
问题 I'm new to immutable.js and I'd like to understand better how to use records starting from a raw JS object. With Immutable.fromJS() I can create a map passing a raw object, for example: var images = { "1": { id: "1", urls: ["/medium/1.jpg", "/large/1.jpg"] }, "2": { id: "2", urls: ["/medium/1.jpg", "/large/1.jpg"] } } var imagesMap = Immutable.fromJS(images); imagesMap is now a map containing other maps, one for each image. I'd like instead to create a map containing records, for example
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