computed-properties

问题 I am bit confused if we can create computed property which is read-only Somethig like: extension ToMyClass { private(set) var isEmpty: Bool { return head == nil } } While trying to create I got following error: error: 'private(set)' modifier cannot be applied to read-only properties 回答1: You are trying to set a modfier for a computed property, which is always read-only The code below was taken from: The Swift Programming Language (Swift 4) struct TrackedString { private(set) var numberOfEdits

问题 This question already has answers here : Ember.js 2.3 implement @each.property observer on a HasMany relationship? (2 answers) Closed 3 years ago . I have to access a property that is two level's deep on my controller, but the [] only can access one level deep via the emberjs guide. model(params) { params.paramMapping = { page: "page", perPage: "per_page", total_pages: "pages" }; return this.findPaged('contractf', params); }, setupController(controller, model) { model.forEach(function(item) {

问题 I have run into a bit of a snag. @StephenThomas graciously helped me with this issue: Vue.js only show objects with a unique property but I need to tweak it a bit more. I am creating a leaderboard for a game. I am using Firestore and I have a collection titled "leaderboard" that keeps all the teams scores. The teams have a start time. Next every time an entry is made for that team the difference in time from the start to now is put in a property titled "diff". In addition, all entries are

问题 Why in earlier when we invoke self in a computed property like this example we would need to write lazy var but now we don't have to. why? let(lazy var in earlier times) pauseButton: UIButton = { let button = UIButton(type: .system) let image = UIImage(named: "pause") button.setImage(image, for: .normal) button.translatesAutoresizingMaskIntoConstraints = false button.tintColor = .white button.addTarget(self, action: #selector(handlePause), for: .touchUpInside) return button }() 回答1: I think

问题 Seems I am quite confused by computed properties in JavaScript. When I define an object and I put [d] as a key (as a property key/name) what does this [d] actually do? Seems that for some values d it calculates s = d.toString() and uses that value s as the property key. But for other values d (e.g. when d is a symbol) it uses really the symbol's value as the key. So this dual behavior of [d] (as a syntax construct) seems confusing. Could someone explain in depth how this works? Are there

问题 I have a YAML file ( all.yaml ) that looks like: ... var1: val1 var2: val2 var3: {{var1}}-{{var2}}.txt ... If I load it in Python like this: import yaml f = open('all.yaml') dataMap = yaml.safe_load(f) f.close() print(dataMap["var3"]) the output is {{var1}}-{{var2}}.txt and not val1-val2.txt . Is it possible to replace the nested vars with the value? I tried to load it with: import jinja2 templateLoader = jinja2.FileSystemLoader( searchpath="/path/to/dir" ) templateEnv = jinja2.Environment(

问题 I am analyzing analyzing some third party code and there is a "lazy" var statement that looks like this, and I would like to understand what the parenthesis are doing after the "computed property" curly braces: lazy var defaults:NSUserDefaults = { return .standardUserDefaults() }() The "return .standardUserDefaults()" is returning the NSUserDefaults instance object, so why add a () after the right curly brace? thanks 回答1: It means that its a block that is executed the first time defaults is

问题 Are lazy vars in Swift computed more than once? I was under the impression that they replaced the: if (instanceVariable) { return instanceVariable; } // set up variable that has not been initialized Paradigm from Objective-C (lazy instantiation). Is that what they do? Basically only called once the first time the app asks for the variable, then just returns what was calculated? Or does it get called each time like a normal computed property? The reason I ask is because I basically want a

问题 I have a table that renders based on computed properties like this. Notice how each row gets its style based on its contents. This works dandy. computed: { rows: function () { return this.$store.getters.tableRows; }, ... } <tr v-for="row in rows" v-bind:class="rowClass(row)"> <td v-for="(item, key, index) in row.columns" v-bind:class="classy(index)">{{item}}</td> </tr> I also wanted to add a collective info outside of the table, so I set up the following messaging conditional. computed: {

问题 I am building a Leaderboard. I have a collection of leaders. There are multiple entries from the same teams. I would like to only show one entry per team (most recent preferably). I am using Firestore for the database. My html looks like this. (I shortened the code for simplicity) <div v-for="tracker in trackers" :key="tracker.id"> <div>{{tracker.team.team_name}}</div> </div> If I add this {{ tracker }} to the HTML this is what one tracker splits out { "team": { "bio": "<div><!--block-->This