optional | 易学教程

npm WARN optional SKIPPING OPTIONAL DEPENDENCY: fsevents

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【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> 场景重现 npm install --verbose 安装依赖的时,出现如下警告 npm WARN optional SKIPPING OPTIONAL DEPENDENCY: fsevents@1.2.4 (node_modules\fsevents): npm WARN notsup SKIPPING OPTIONAL DEPENDENCY: Unsupported platform for fsevents@1.2.4: wanted {"os":"darwin","arch":"any"} (current: {"os":"win32","arch":"x64"}) npm verb notsup SKIPPING OPTIONAL DEPENDENCY: Valid OS: darwin npm verb notsup SKIPPING OPTIONAL DEPENDENCY: Valid Arch: any npm verb notsup SKIPPING OPTIONAL DEPENDENCY: Actual OS: win32 npm verb notsup SKIPPING OPTIONAL DEPENDENCY: Actual Arch: x64 释疑这不是什么真的有问题

unexpectedly found nil while unwrapping an Optional value reading JSON

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问题 people, I can not understand why, but this problem (unexpectedly found nil while unwrapping an Optional value) happens in this line: var dict: NSDictionary = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: &error) as NSDictionary see the code: import Foundation class ProdutoService { // return a produtos Array class func getProdutos() -> Array<Produto> { var produtos: Array<Produto> = [] for (var i = 0; i < 10; i++) { var p = Produto() p

optional variable in class definition

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问题 optionals in class definition I have a 'mastermodel' from which most of my models inherit so they can have the configuration constants class MasterModel { static let apiKey = (drop.config["app","thinx-api-key"]?.string)! static let baseURL = (drop.config["app","base-URL"]?.string )! } Notice the force unwraps :( In this case it's not really a huge problem as the program won't start without these constants but I'd like to clean this up anyway. guard statements are only allowed in functions,

iOS中使用Protocol Buffers

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【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> Google Protocol Buffer (简称 Protobuf )是由Google推出的一种轻便高效的结构化数据存储格式，可以用于结构化数据串行化，或者说序列化。它很适合做数据存储或RPC数据交换格式。可用于通讯协议、数据存储等领域的语言无关、平台无关、可扩展的序列化结构数据格式。 Protocol buffers are a language-neutral, platform-neutral extensible mechanism for serializing structured data. Protobuf和XML相比同是数据交换协议，不过Protobuf更小、更快、也更简单。可以通过定义自己的数据结构，然后使用Protobuf的代码生成器生成代码，用生成的代码来读写这个数据结构。Protobuf具有如下几个优点： (1)“向后”兼容性好。不必担心因为消息结构的改变而造成的大规模的代码重构或者迁移的问题，因为添加新的消息中的字段并不会引起已经发布的程序的任何改变。 (2)语义更清晰。Protobuf使用 .proto 文件描述数据交换的格式，然后Protobuf编译器会将 .proto 文件编译生成对应的数据访问类以对 Protobuf 数据进行序列化、反序列化操作），无需解释器之类的东西。

Java 8 Stream 的终极技巧——Collectors 操作

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【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> 1. 前言昨天在 Collection移除元素操作相关的文章中提到了 Collectors 。相信很多同学对这个比较感兴趣，那我们今天就来研究一下 Collectors 。 2. Collectors 的作用 Collectors 是 Java 8 加入的操作类，位于 java.util.stream 包下。它会根据不同的策略将元素收集归纳起来，比如最简单常用的是将元素装入 Map 、 Set 、 List 等可变容器中。特别对于 Java 8 Stream Api 来说非常有用。它提供了 collect() 方法来对 Stream 流进行终结操作派生出基于各种策略的结果集。我们就借助于 Stream 来熟悉一下 Collectors 吧。我们依然用昨天的例子： List<String> servers = new ArrayList<>(); servers.add("Felordcn"); servers.add("Tomcat"); servers.add("Jetty"); servers.add("Undertow"); servers.add("Resin"); 3. Java 8 中 Collectors 的方法 Collectors 提供了一系列的静态方法供我们使用

iOS - Swift and Parse error regarding Optionals within Subclass

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问题 I have implemented a Parse subclass called Filler.swift that contains five variables that are held in the Parse backend. Whilst trying to save data to the Parse backend using this subclass I get the error: fatal error: unexpectedly found nil while unwrapping an Optional value . This is the code that brings about the error (on the self.object.username = username line): if let username = PFUser.currentUser()?.username { // set username equal to current user self.object.username = username }else

URL array throwing optional error swift

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问题 I am not sure how to resolve the optional type error that occurs at "if let imageURL = imageFile.path" in my code below. The error it throws is "Initializer for conditional binding must have Optional type, not 'String'" After googling, I'm guessing it has something to do with the directoryContentsArray = URL I set at the beginning of my CollectionViewController class. Please help! P.S. Sorry for the repeat optional error question, but I'm super confused :/ class CollectionViewController:

Handling exceptions while returning values by Optional flatmap

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问题 I have tried implementing Optional from JAVA in the below code. getOrders() method throws a KException. @Override public Optional<List<Order>> getPendingOrders(AuthDTO authDTO) throws MyException { List<Order> orders=null; try { Optional<KConnect> connection = connector.getConnection(authDTO); if (connection.isPresent()) { orders = connection.get().getOrders(); } }catch (KException e){ throw new MyException(e.message,e.code); } return Optional.ofNullable(orders); } I tried to remove the

Handling exceptions while returning values by Optional flatmap

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Java 8 conditional .map() (or map with identity function)

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问题 Suppose we have boolean flag to turn on/off map in a stream. For example to trim or not. Are the below examples proper solution or there is a better way to implement that? boolean doTrim = true; optionalValue.map(doTrim ? String::trim : (x) -> x ).get()... or: boolean doTrim = true; optionalValue.map(doTrim ? String::trim : Function.identity() ).get()... 回答1: You are over-complicating things. If you have an Optional<String> optionalValue you can simply say: if(doTrim) optionalValue