golang error catching

Golang is a strongly typed programming language that provides a good error handling mechanism at the language level. Error handling is an essential part of the Golang development process. Its design concept is to separate error handling from the code and business logic to achieve more readable and maintainable code.

In Golang, the basis of the error mechanism is a built-in type - error. error is an interface type in Golang. It defines a method: Error(), which is used to return error information. errorThe expected exception can be passed to the caller as the return value of the function, or as a parameter to the call of other functions.

When an error occurs in a function, it will return a non-nil error object that contains error information. The caller can determine whether the function has been executed successfully by checking the returned error. If nil is returned, it means that the function execution was successful; otherwise, it means that the function execution failed.

Below, we will introduce some common error handling mechanisms and techniques in Golang:

1. Use defer and recover

defer mechanism to delay The execution of a function is not executed until the function returns. deferCommonly used for operations such as releasing resources, closing files, clearing buffers, etc. recover is used to restore the program control flow after [panic](https://tour.golang.org/basics/13) so that the program can continue to execute normally. It can only be called in defer, otherwise it will not work.

In Golang, you can use the defer and recover mechanisms to implement error handling, that is, use recover# in the defer statement ##To capture the error information generated during function execution, then determine the error type and handle it accordingly.

func processFile(filename string) error {
    file, err := os.Open(filename)
    if err != nil {
        return err
    }
    defer file.Close()

    // Read the file here...

    return nil
}

func main() {
    err := processFile("/path/to/myfile.txt")
    if err != nil {
        // Handle the error here...
        fmt.Println(err)
    }
}

defer; and finally nil Return, indicating that the function was executed successfully. In the main function, if the calling function returns a non-nil error, it means that the function execution failed, so we need to perform corresponding error handling operations.

Error() method. Custom error types can make the code more readable and reduce the possibility of errors; at the same time, it can also improve code reusability.

type customError struct {
    message string
    code    int
}

func (e *customError) Error() string {
    return fmt.Sprintf("%s [%d]", e.message, e.code)
}

func processFile(filename string) error {
    file, err := os.Open(filename)
    if err != nil {
        return &customError{"Error opening file", 1001}
    }
    defer file.Close()

    // Read the file here...

    return nil
}

func main() {
    err := processFile("/path/to/myfile.txt")
    if err != nil {
        // Handle the error here...
        fmt.Println(err)
    }
}

customError, which contains the error message and error code. In the processFile() function, if the file cannot be opened, a customError object is returned. In the main function, if an error occurs, call the Error() method to obtain the error information.

Don’t ignore the return value: In Golang, functions return values There can be multiple, and returning an error is a very common situation. Ignoring the return value will cause the code to be unable to determine whether the function is successfully executed, resulting in errors that are difficult to troubleshoot, making it difficult to control the code quality.
• Use package-level variables: In Golang, package-level variables are visible and accessed by the entire package, and global error information can be saved there. Developers can modify these variables through specific functions to record the correctness, robustness, and fault tolerance of the code.
• Don't nest errors deeply: If there are multiple nested function calls, the error message should be hierarchically returned along the call stack, and finally handled in the top-level function. This ensures code readability.
• Do not use ID or description information as part of the error type. Instead, use a clearer and more meaningful error type.
• Add additional context words to the error message: Add contextual information to the error message to make it easier for the error handling code to identify the error.

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