Kotlin's delegation model is built on the idea of delegation by delegation. In this pattern, one object (the delegate) is responsible for handling a request from another object (the delegator). The delegator can delegate all or part of its responsibilities to the delegate.
In Kotlin, delegation is a first-class language feature. You can use delegation to implement common design patterns, such as the Observer pattern, the Decorator pattern, and the Factory pattern. Delegation can also be used to improve the performance of your code.
In this post, we'll take a closer look at delegated properties in Kotlin. We'll learn how to create and use delegated properties, and we'll explore some of the benefits of using delegation.
A delegated property is a property whose value is computed by a delegate. A delegate is an object that knows how to compute the value of a property. In Kotlin, you can create a delegated property by using the by
keyword.
For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by lazy {
// compute the name
}
}
In this example, the name
property is a delegated property. The delegate is an instance of the Lazy
class. The Lazy
class knows how to compute the value of the name
property.
When you access the name
property, the Lazy
instance will compute the value of the property and return it. The value will be cached, so that subsequent accesses to the property will be fast.
##Creating Delegated Properties
As we saw in the previous section, you can create a delegated property by using the by
keyword. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by lazy {
// compute the name
}
}
In this example, the name
property is a delegated property. The delegate is an instance of the Lazy
class. The Lazy
class knows how to compute the value of the name
property.
When you access the name
property, the Lazy
instance will compute the value of the property and return it. The value will be cached, so that subsequent accesses to the property will be fast.
You can also create a delegated property by using a property delegate. A property delegate is an object that knows how to compute the value of a property. In Kotlin, you can create a property delegate by using the by
keyword.
For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using a property delegate:
class User {
val name: String by NameDelegate()
}
In this example, the name
property is a delegated property. The delegate is an instance of the NameDelegate
class. The NameDelegate
class knows how to compute the value of the name
property.
When you access the name
property, the NameDelegate
instance will compute the value of the property and return it. The value will be cached, so that subsequent accesses to the property will be fast.
In Kotlin, you can create a delegate by using the by
keyword. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by lazy {
// compute the name
}
}
In this example, the name
property is a delegated property. The delegate is an instance of the Lazy
class. The Lazy
class knows how to compute the value of the name
property.
When you access the name
property, the Lazy
instance will compute the value of the property and return it. The value will be cached, so that subsequent accesses to the property will be fast.
You can also create a delegate by using a property delegate. A property delegate is an object that knows how to compute the value of a property. In Kotlin, you can create a property delegate by using the by
keyword.
For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using a property delegate:
class User {
val name: String by NameDelegate()
}
In this example, the name
property is a delegated property. The delegate is an instance of the NameDelegate
class. The NameDelegate
class knows how to compute the value of the name
property.
When you access the name
property, the NameDelegate
instance will compute the value of the property and return it. The value will be cached, so that subsequent accesses to the property will be fast.
In Kotlin, you can use the by
keyword to delegate to a map. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by mapOf("id" to 1, "name" to "John")
}
In this example, the name
property is a delegated property. The delegate is a map. When you access the name
property, the map will be searched for the key name
. If the key is found, the corresponding value will be returned. If the key is not found, an exception will be thrown.
In Kotlin, you can use the by
keyword to delegate to a property. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by lazy {
firstName + " " + lastName
}
}
In this example, the name
property is a delegated property. The delegate is a property. When you access the name
property, the firstName
and lastName
properties will be accessed and concatenated. The result will be returned.
In Kotlin, you can use the by
keyword to delegate to a function. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by lazy {
computeName()
}
}
In this example, the name
property is a delegated property. The delegate is a function. When you access the name
property, the computeName()
function will be called. The result will be returned.
In Kotlin, you can use the by
keyword to delegate to an object. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by NameDelegate()
}
In this example, the name
property is a delegated property. The delegate is an object. When you access the name
property, the NameDelegate
object will be used to compute the value of the property. The result will be returned.
In Kotlin, you can use the by
keyword to delegate to a class. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by lazy {
NameDelegate.computeName()
}
}
In this example, the name
property is a delegated property. The delegate is a class. When you access the name
property, the NameDelegate.computeName()
method will be called. The result will be returned.
In Kotlin, you can use the by
keyword to delegate to a superclass. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User : SuperUser() {
val name: String by lazy {
super.name
}
}
In this example, the name
property is a delegated property. The delegate is the name
property of the superclass. When you access the name
property, the name
property of the superclass will be accessed. The result will be returned.
In Kotlin, you can use the by
keyword to delegate to a companion object. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by lazy {
User.name
}
}
In this example, the name
property is a delegated property. The delegate is the name
property of the companion object. When you access the name
property, the name
property of the companion object will be accessed. The result will be returned.
In Kotlin, you can use the by
keyword to delegate to an interface. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by NameDelegate()
}
In this example, the name
property is a delegated property. The delegate is an interface. When you access the name
property, the NameDelegate
interface will be used to compute the value of the property. The result will be returned.
In Kotlin, you can use the by
keyword to delegate to an abstract class. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by lazy {
NameDelegate.computeName()
}
}
In this example, the name
property is a delegated property. The delegate is an abstract class. When you access the name
property, the NameDelegate.computeName()
method will be called. The result will be returned.
In Kotlin, you can use the by
keyword to delegate to an object literal. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by mapOf("id" to 1, "name" to "John")
}
In this example, the name
property is a delegated property. The delegate is an object literal. When you access the name
property, the map will be searched for the key name
. If the key is found, the corresponding value will be returned. If the key is not found, an exception will be thrown.
In Kotlin, you can use the by
keyword to delegate to a nested class. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by lazy {
NestedClass.name
}
}
In this example, the name
property is a delegated property. The delegate is a nested class. When you access the name
property, the NestedClass.name
property will be accessed. The result will be returned.
In Kotlin, you can use the by
keyword to delegate to an inner class. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by lazy {
InnerClass.name
}
}
In this example, the name
property is a delegated property. The delegate is an inner class. When you access the name
property, the InnerClass.name
property will be accessed. The result will be returned.
In Kotlin, you can use the by
keyword to delegate to an anonymous object. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by lazy {
object: NameDelegate {
override fun computeName(): String {
// compute the name
}
}
}
}
In this example, the name
property is a delegated property. The delegate is an anonymous object. When you access the name
property, the computeName()
method of the anonymous object will be called. The result will be returned.
In Kotlin, you can use the by
keyword to delegate to a lambda. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by lazy {
// compute the name
}
}
In this example, the name
property is a delegated property. The delegate is a lambda. When you access the name
property, the lambda will be called. The result will be returned.
In Kotlin, you can use the by
keyword to delegate to a method reference. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name. You could create this property by using the by
keyword:
class User {
val name: String by lazy {
User::name
}
}
In this example, the name
property is a delegated property. The delegate is a method reference. When you access the name
property, the name
method of the User
class will be called. The result will be returned.
In Kotlin, you can use the by
keyword to delegate to a constructor. For example, suppose you have a class that represents a user. You might want to create a property that stores the user's name