The API in the Go language should be clear, stable, easy to use, and have good scalability and maintenance. 1. Clarify responsibilities and boundaries. A function or interface only does one thing. Use middleware or helper functions to decouple non-core logic, and name it accurately reflects the function. 2. The return value and error handling should be unified, and the result and error are returned in (T, error) form, customize the error type and provide meaningful error information. 3. Interface design should be conducive to testing and replacement, abstracting the mutable part into an interface, and the constructor accepts interface parameters to implement replacement, avoiding global variables and hard-coded dependencies. 4. Take into account performance and simplicity, optimize memory allocation and performance bottlenecks in high-frequency scenarios, but choose a clearer way in low-frequency scenarios.

When designing APIs in Go, the core goal is to make the interface clear, stable, and easy to use, while having good scalability and maintenance. Go's philosophy of simplicity determines that we should not overly abstract or complicate when designing APIs, but should focus on practicality.

1. Clarify responsibilities and boundaries

The first priority of an API is to clarify its scope of responsibility. A function or interface should do only one thing and do it well. For example, when processing HTTP requests, each handler should focus on handling specific business logic, rather than other operations such as mixed data conversion and logging.

suggestion:

• Avoid doing too many things in one function
• Use middleware or helper functions to decouple non-core logic
• Interface naming should accurately reflect its functions, such as CreateUser instead of HandleUser

For example, if you have an API that handles user registration, it should not be responsible for sending mail or writing audit logs at the same time. These can be processed asynchronously asynchronously as subsequent actions through event notifications, etc.

2. Design of return value and error handling

Go's multi-return value mechanism is ideal for returning results and error messages. When designing APIs, unify error handling to avoid "hiding" errors or forcing callers to ignore them.

Common practices:

• Always return possible error results in the form of (T, error)
• Customize error types for easy identification and processing by callers (such as ErrInvalidInput )
• The error message should be meaningful, don't just error: something went wrong

For example:

 func GetUser(id string) (*User, error) {
    if id == "" {
        return nil, fmt.Errorf("user ID is required")
    }
    // ...
}

This design allows the caller to know clearly that the function may fail and can respond to different errors.

3. Interface design should be conducive to testing and replacement

A good API design should be testable. This means you need to consider how to mock the interface dependencies and how to inject dependencies. Go's interface system is ideal for loosely coupled designs.

Key points:

• Abstracting variable parts into interfaces, such as database access and external service calls
• The constructor accepts interface parameters for easy replacement implementation
• Try to avoid package-level global variables or hard-coded dependencies

For example, if you have a service that sends text messages, you can design it like this:

 type SMSSender interface {
    Send(phone, message string) error
}

func NotifyUser(sender SMSSender, phone string) error {
    return sender.Send(phone, "Welcome!")
}

This way you can pass in the mock implementation in the test without actually sending a text message.

4. Take into account performance and simplicity

Go is a language that emphasizes performance, so you should consider efficiency when designing APIs. But you cannot sacrifice code readability and maintenance for performance.

Practical suggestions:

• Avoid unnecessary memory allocations, such as reusing buffers or object pools
• Perform performance analysis of high-frequency calls to optimize bottlenecks
• Don't optimize too early, make sure the logic is correct and clear

For example, when dealing with large number of string splicing, use strings.Builder than directly More efficient; but in low-frequency scenarios, the two are not much different, so a clearer way is preferred.

Basically that's it. Designing an API does not require too complex techniques. The key is to understand the needs of users, maintain consistency, and make reasonable abstractions in the right places.

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