lazy-initialization | 易学教程

On lazy instantiation and convenience methods

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Assume you have a Singleton Constants class, instance of which you'd like to use throughout your application. In someClass , therefore we can reference [Constants instance] someCleverConstant]; Typing this gets old really quick and it would be nice to get a shortcut to the instance. In someClass , we can declare @property (nonatomic, weak, readonly) Constants *constants; And a getter to the instance -(Constants*) constants { if (constants == nil) constants = [Constants instance]; return constants; } This way in someClass, therefore we can reference constants.someCleverConstant; instead A few

Lazy Evaluation: Why is it faster, advantages vs disadvantages, mechanics (why it uses less cpu; examples?) and simple proof of concept examples [closed]

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Lazy evaluation is said to be a way of delaying a process until the first time it is needed. This tends to avoid repeated evaluations and thats why I would imagine that is performing a lot faster. Functional language like Haskell (and JavaScript..?) have this functionality built-in. However, I don't understand how and why other 'normal' approaches (that is; same functionality but not using lazy evaluation) are slower.. how and why do these other approaches do repeated evaluations? Can someone elaborate on this by giving simple examples and explaining the mechanics of each approach? Also,

Why do RelayCommands typically use lazy initialization?

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When using Josh Smith's RelayCommand , most of the examples I've seen use lazy initialization such as: public class ViewModel { private ICommand myCommand; public ICommand MyCommand { get { if (myCommand == null) { myCommand = new RelayCommand(p => DoSomething() ); } return myCommand; } } // ... stuff ... } Rather than creating the RelayCommand in the constructor, like this: public class ViewModel { public ViewModel() { MyCommand = new RelayCommand(p => DoSomething()); } public ICommand MyCommand { get; private set; } // ... stuff ... } What's the benefit of using lazy initialization here? It

Lazy loading Angular views and controllers on page scroll

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I have a microsite that is utilizing Laravel and Angular. It's a one page microsite that is responsive and is broken into 5 sections. I would like to lazy load them to cut down on loading all at once. <body ng-app> <div id="wrapper"> <section id="intro">1</section> <section id="Second">2</section> <section id="Third">3</section> <section id="Fourth">4</section> <section id="Fifth">5</section> </div> </body> I'm looking to load 1 & 2 on page load then as you scroll down the page load the other view with a nice fade in and then load its interactive items. In this case it is probably not

Singleton lazy vs eager instantiation

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问题 If a singleton is implemented as follows, class Singleton { private static Singleton instance = new Singleton(); public static Singleton getInstance() { return instance; } } How is this implementation different from the lazy initialization approach? In this case,the instance will be created when the class is loaded and the class itself is loaded only on the first active use (for example, Singleton.getInstance() not when you declare for instance Singleton singleton = null;) Even with lazy

C++ different singleton implementations

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问题 I usually implement the singleton pattern this way : class Singleton { public: virtual ~Singleton() {} static Singleton& GetInstance() { static Singleton instance; return instance; } private: Singleton(); Singleton(const Singleton&); Singleton& operator=(const Singleton&); } Recently, I ran into this implementation, which is slightly different : class Singleton { public: Singleton(); virtual ~Singleton() {} static Singleton& GetInstance() { return instance; } private: Singleton(const

Are lazy vars in Swift computed more than once?

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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 computed property in Swift that can access other instance variables. Say I have a variable called "fullName

Lazy initialisation and retain cycle

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While using lazy initialisers, is there a chance of having retain cycles? In a blog post and many other places [unowned self] is seen class Person { var name: String lazy var personalizedGreeting: String = { [unowned self] in return "Hello, \(self.name)!" }() init(name: String) { self.name = name } } I tried this class Person { var name: String lazy var personalizedGreeting: String = { //[unowned self] in return "Hello, \(self.name)!" }() init(name: String) { print("person init") self.name = name } deinit { print("person deinit") } } Used it like this //... let person = Person(name: "name")

Why do RelayCommands typically use lazy initialization?

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问题 When using Josh Smith's RelayCommand, most of the examples I've seen use lazy initialization such as: public class ViewModel { private ICommand myCommand; public ICommand MyCommand { get { if (myCommand == null) { myCommand = new RelayCommand(p => DoSomething() ); } return myCommand; } } // ... stuff ... } Rather than creating the RelayCommand in the constructor, like this: public class ViewModel { public ViewModel() { MyCommand = new RelayCommand(p => DoSomething()); } public ICommand

LazyInitializationException in selectManyCheckbox on @ManyToMany(fetch=LAZY)

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What is the best way to handle multiple chackboxes when you nead to fill a JPA M:N relation ... for example I have an JPA entity Hardware and the entity Connectivity. Hardware has a set for connectivity : private Set<Connectivity> connectivities = new HashSet<Connectivity>(0); and has a setter and getter like this : @ManyToMany(fetch = FetchType.LAZY, cascade = { CascadeType.PERSIST, CascadeType.REFRESH }, mappedBy = "hwProviders") public Set<Connectivity> getConnectivities() { return this.connectivities; } public void setConnectivities(Set<Connectivity> connectivities) { this.connectivities =