In software development, we often encounter situations where we need to dynamically select algorithms or behaviors. In order to avoid using a large number of conditional statements in the code (such asif-elseorswitch case),Strategy PatternIt provides an elegant solution. Through the strategy pattern, we can encapsulate algorithms or behaviors into independent classes and switch them freely at runtime. This article will introduce the concept of strategy pattern, the difference between it and other similar patterns, the problems it solves, implementation examples in Golang, and its application and precautions in actual development.

What is Strategy Pattern?

Strategy Patternis aBehavioral design patterns, which defines a series of algorithms and encapsulates them into independent strategy classes so that they can be replaced with each other.The Strategy pattern separates the use of an algorithm from its implementation,The client does not need to care about the specific algorithm implementation, but only needs to select the required strategy.

Components of the Strategy Pattern

1. Strategy Interface: Defines the common interface for all policies.
2. Concrete Strategy: Implement the specific algorithm or behavior of the strategy interface.
3. Context: Responsible for holding the strategy object and calling the strategy method when needed.

Differences between Strategy Pattern and other Patterns

1. Template Method Pattern

• Target: The Template Method pattern defines the framework of an algorithm and allows subclasses to override the implementation of certain steps.
• the difference: The algorithm structure of the template method pattern is fixed, while the strategy pattern allows different algorithms to be selected at runtime.

2. State Pattern

• Target: The state pattern changes the behavior of an object based on its state changes.
• the difference: The state pattern focuses onState Transition, while the strategy pattern focuses onAlgorithm selection and switching.

3. Factory Method Pattern

• Target: The factory method pattern is used to create objects and decouple the instantiation logic from the client code.
• the difference: The strategy pattern focuses on the encapsulation and replacement of algorithms, while the factory method pattern focuses on the creation of objects.
• The factory method mode can be found in the following blog post:
  In-depth analysis of Go design pattern simple factory pattern: implementation and application in Golang
  In-depth analysis of Go design pattern factory method pattern: implementation and application in Golang
  In-depth analysis of Go design pattern abstract factory pattern: implementation and application in Golang

What problem does the strategy pattern solve?

1. Eliminate complex conditional judgments: Encapsulate different algorithms into independent strategy classes to avoid using a large number ofif-elseorswitch casestatement.
2. Improve code scalability：When adding a new algorithm, you only need to implement a new strategy class without modifying the original code, which is in line withOpen/Closed Principle.
3. Flexible replacement of algorithms: Freely switch strategies at runtime to implement flexible business logic.

Application scenarios of strategy pattern

1. Payment Systems：Use different payment strategies to process according to the payment method selected by the user (such as Alipay, WeChat, credit card).
2. Data Compression: Different compression algorithms (such as ZIP, RAR, GZIP) can be encapsulated as policy classes, and users can choose which compression policy to use according to their needs.
3. Sorting Algorithms: Choose different sorting strategies (such as quick sort, bubble sort) according to the characteristics of the data.
4. Permission verification: Different permission verification logics can be encapsulated as strategies for flexible application in different scenarios.

Strategy pattern implementation in Golang

The following is a specific Golang example showing how to use the strategy pattern to implement a simplePayment Systems. Users can choose different payment methods (such as Alipay, WeChat, credit card) to make payment.

Example: Payment system

1. Define the strategy interface

package main import "fmt" // PaymentStrategy interface: defines payment strategy type PaymentStrategy interface { Pay(amount float64) }

2. Implement specific payment strategies

// Alipay struct: Alipay payment type Alipay struct{} func (a *Alipay) Pay(amount float64) { fmt.Printf("Paid %.2f using Alipay.\n", amount) } // WeChatPay struct: WeChat payment type WeChatPay struct{} func (w *WeChatPay) Pay(amount float64) { fmt.Printf("Paid %.2f using WeChatPay.\n", amount) } // CreditCard struct: Credit card payment type CreditCard struct { CardNumber string } func (c *CreditCard) Pay(amount float64) { fmt.Printf("Paid %.2f using Credit Card %s.\n", amount, c.CardNumber) }

3. Define the context class

// PaymentContext structure: holds the payment strategy and calls its methods type PaymentContext struct { strategy PaymentStrategy } func (p *PaymentContext) SetStrategy(strategy PaymentStrategy) { p.strategy = strategy } func (p *PaymentContext) Pay(amount float64) { p.strategy.Pay(amount) }

4. Sample code using the strategy pattern

func main() { // Create a context object payment := &PaymentContext{} // Use Alipay to pay payment.SetStrategy(&Alipay{}) payment.Pay(100.00) // Use WeChat to pay payment.SetStrategy(&WeChatPay{}) payment.Pay(200.00) // Use a credit card to pay payment.SetStrategy(&CreditCard{CardNumber: "1234-5678-9012-3456"}) payment.Pay(300.00) }

Output

Paid 100.00 using Alipay. Paid 200.00 using WeChatPay. Paid 300.00 using Credit Card 1234-5678-9012-3456.

Code Analysis

1. PaymentStrategy Interface: Defines the common interface for all payment strategiesPay.
2. Alipay, WeChatPay and CreditCard: Specific strategy classes implement the payment logic of Alipay, WeChat and credit card respectively.
3. PaymentContext Structure: Holds the payment strategy and passesSetStrategyMethod dynamically switches strategies.
4. main function: Demonstrates how to achieve flexible payment method switching through the strategy pattern.

Application in actual development

1. Payment Gateway: In the e-commerce system, different payment gateways can be encapsulated into different strategy classes, and users can freely choose the payment method.
2. Logging System: Different logging methods (such as files, consoles, and databases) can be encapsulated as strategies to switch log output methods at runtime.
3. Data encryption: During data transmission, different encryption algorithms (such as AES and DES) are selected according to needs and encapsulated as policy classes.
4. Path Planning: In map applications, different path planning strategies (such as shortest path, avoiding highways, and scenery priority) can be selected according to user needs.

Things to note when using the strategy pattern

1. Avoid too many strategies: If there are many types of algorithms, the number of strategy classes may increase rapidly, and the code structure needs to be designed reasonably.
2. Reasonable design of interface: The strategy interface should be kept as simple as possible to avoid excessive complex logic.
3. Performance overhead: If the strategy is switched too frequently, it may cause certain performance overhead.

Comparison between Strategy Pattern and Template Method Pattern

Summarize

Strategy PatternIt is a very flexible design pattern. By encapsulating algorithms or behaviors into independent strategy classes, flexible replacement and dynamic switching of algorithms are achieved. In Golang, the implementation of the strategy pattern is very simple.Interfaces and structuresIn actual development, the strategy pattern is widely used in payment systems, log systems, data encryption, and path planning. If you need to flexibly switch algorithms or behaviors in your project, the strategy pattern will be a very suitable solution.

Reference Links

• Design Patterns - Strategy Pattern
• Golang Design Patterns