Error type application tips for Golang functions

In the Golang language, functions are a key part of the basic implementation logic, and error handling is an important aspect of most functions. Golang provides a powerful error handling mechanism through the Error type. In this article, we will explore the Error type application skills of Golang functions.

1. Understanding Golang’s Error type

In Golang, Error is an interface type with only one Error() method:

type error interface {
    Error() string
}

Any type only needs to implement the Error method It can become an error type. This method returns a string summarizing the reason for the error. Therefore, the Error type plays a unified role in handling errors in Golang.

2. Returning errors

Function is an important part of Golang. However, when a function returns an error, Golang usually uses a separate return value to indicate the error. For example, during file operations, if the operation fails, an error is returned. Common file operation functions are as follows:

func Open(name string) (*File, error) 
func (f *File) Read(b []byte) (n int, err error)
func (f *File) Write(b []byte) (n int, err error)
fucn (f *File) Seek(offset int64, whence int) (ret int64, err error)

The last value returned by these functions is usually error. We can make our code more robust by returning an appropriate error type to handle errors.

After returning an error, use syntax similar to the following to handle it:

_, err := f.Read(b)
if err != nil {
    log.Fatal(err)
}

In this example, if there is an error reading the file, the program will issue an "err" log.

3. Comparison of error types

In Golang, there are three ways to compare error types.

1. Use strings for comparison

We can compare error strings with other strings to produce corresponding actions:

if err.Error() == "file not found" {
    return
}

2. Use specific errors Type comparison

For some specific error types, we can use type assertions to compare them. For example, suppose we have a function DoSomething which returns a specific error type, we can check the error type using type assertion as follows:

_, err := DoSomething()
if e, ok := err.(*CustomError); ok {
    fmt.Println(e.CustomMessage)
}

If an error occurs while DoSomething is executed, then use type assertion to check the error type . If the returned error type is CustomError, CustomMessage will be output to the console.

3. Use error codes for comparison

Finally, we can use error codes to compare error types. The error code is a custom constant, usually included in a custom error type. Here is an example:

const (
    ErrCodeFileNotFound = iota + 1
    ErrCodeInvalidParam
)

type CustomError struct {
    Code          int
    CustomMessage string
}

func (e *CustomError) Error() string {
    return fmt.Sprintf("%d:%s", e.Code, e.CustomMessage)
}

func DoSomething() error {
    return &CustomError{
        Code:          ErrCodeFileNotFound,
        CustomMessage: "file not found",
    }
}

func main() {
    err := DoSomething()
    if e, ok := err.(*CustomError); ok && e.Code == ErrCodeFileNotFound {
        fmt.Println(e.CustomMessage)
    }
}

In this example, we define two error code constants (ErrCodeFileNotFound and ErrCodeInvalidParam) and use them to compare error types. Then we define a custom error type, CustomError, which contains the error code and custom message. Finally, we define a function DoSomething that returns an instance of type CustomError.

Finally, we use the error code in main to compare the error type and print the corresponding error message.

In short, Golang’s Error type is a powerful way to handle errors. With the right error types, we can better handle various error conditions, making our code more robust and efficient.

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