Reading design patterns adapter patterns

Adapter（ Adapter pattern ）

Adapter（ Adapter pattern ） It's a structural model , Alias wrapper, Structural patterns focus on how to combine classes and objects , To get a bigger structure , We usually work with this design pattern most of the time .

Intention ： Converts the interface of a class to another interface that the customer wants .Adapter Patterns allow classes that cannot work together because of incompatible interfaces to work together .

The intention of this design pattern is easy to understand , It is to smooth out the problem of interface incompatibility . Be careful , It can only solve the problem of interface inconsistency , It can't solve the problem of inconsistent functions .

For example

If you don't understand the intention above , It doesn't matter. , Design patterns need to be used in daily work , Combining examples can deepen your understanding , Now I've prepared three examples , Let you understand what scenario will use this design pattern .

Interface Converter

There are many kinds of sockets , We've used a lot of adapters , Switch different plugs , It can be used normally without replacing the socket .

USB Interface conversion is also wonderful , There will be TypeC Interface to TypeA Of , There are also generals TypeA Interface to TypeC Of , Support bidirectional conversion .

Interface converter is the adapter pattern we use in our life , Because the manufacturer didn't make a new socket , We didn't change a mobile phone because the interface didn't fit , All you need is an interface converter , This is the benefit of using design patterns .

database ORM

ORM Shielded SQL This floor , The benefit is that there is no need to understand the difference SQL The difference between grammars , For general functions ,ORM Depending on the platform , such as Postgresql、Mysql Conduct SQL Transformation .

Yes ORM Come on , Shield the differences between different platforms , This is done by using the adapter pattern .

API Deprecated

When a widely used library contains break change When upgrading , It often leaves developers enough time to upgrade , You can't just hang up after upgrading , So the abandoned API To be marked as deprecated, And this kind of abandoned label API The actual implementation of , It's often new API replace , This scenario uses the adapter pattern , New API Adapt to the old API, Realization API Deprecated.

Intention to explain

The above three examples all satisfy the following two conditions ：

API Are not compatible ： Because of the different interfaces ; database SQL Different grammar ; frame API Different .
But the ability has supported ： All sockets have charging or reading capabilities ; Different SQL Have the ability to query the database ; new API Covering the old API The ability of .

In this way, the adapter can satisfy Adapter The intent of the ：

chart

The implementation of the adapter is divided into inheritance and composition patterns .

Here is the explanation of the term ：

Adapter Adapter , hold Adeptee Adaptation Target.
Adaptee Adapted content , For example, incompatible interfaces .
Target Fit to the content of , For example, the interface you need to use .

Inherit ：

Adapter inheritance Adaptee And implement Target, The applicable scenario is Adaptee And Target Similar structure , Because only partial differentiation is needed .

Combine ：

The combination is more expansive , But it's a lot more work , If Target And Adaptee The structure is quite different , It's suitable to use combination mode .

Code example

The following example uses typescript To write .

Inherit ：

`interface ITarget {
// The standard way is hello
hello: () => void
}
class Adaptee {
// The class method to be adapted is called sayHello
sayHello() {
console.log('hello')
}
}
// Adapter inheritance Adaptee And implement ITarget
class Adapter extends Adaptee implements ITarget {
hello() {
// use sayHello Dock to hello
super.sayHello()
}
}`

Combine ：

`interface ITarget {
// The standard way is hello
hello: () => void
}
class Adaptee {
// The class method to be adapted is called sayHello
sayHello() {
console.log('hello')
}
}
// Adapter inheritance Adaptee And implement ITarget
class Adapter implements ITarget {
private adaptee: Adaptee
constructor(adaptee: Adaptee) {
this.adaptee = adaptee
}
hello() {
// use adaptee.sayHello Dock to hello
this.adaptee.sayHello()
}
}`

disadvantages

Using the adapter pattern itself can be a problem , Because a good system should not do any overseas Chinese , Models should be consistent . Consider using the adapter pattern only if ：

New and old systems take over , The cost of retrofitting is very high .
Three way bag fit .
Old and new API compatible .
Unify the interfaces of multiple classes . It can be used in combination with the factory method .

summary

The adapter mode also composes the open close principle , On the premise of not reforming the original object , Build an adapter to complete the module connection .

The implementation of adapter pattern is divided into class pattern and object pattern , Class patterns use inheritance , Object patterns use composition , Apply respectively to Adaptee And Target Scenes with similar structure and great difference in structure , In any case , Combination patterns are the most flexible .

Finally, a diagram is used to summarize the thinking of adapter pattern ：

The address for discussion is ： intensive reading 《 Design patterns - Adapter Adapter pattern 》· Issue #279 · dt-fe/weekly

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