Methods to define custom error types include: 1. Create a structure and implement the Error() method; 2. Extend the structure field to carry more information such as error codes and operation names; 3. Use fmt.Errorf and %w to wrap the original error to preserve the stack information. In Go language, you can create basic custom error types by defining structure types such as MyError or AppError and implementing the Error() string method. You can also expand error information by adding fields such as Code and Op; for advanced usage, you can use fmt.Errorf to combine with %w to wrap the original error into a new error, and use errors.Unwrap or errors.As to extract the original error; in addition, it is recommended to keep the error structure concise, unify the project error structure, avoid duplicate wheels, and pay attention to error checking to improve code quality and troubleshooting efficiency.
In Go, creating custom error types is a great way to improve code readability and maintenance. The error interface in the standard library is enough to handle many situations, but when you need to carry more information (such as error code, location, original error, etc.), custom errors come in handy.
Here are several common ways and precautions to help you better use custom error types in your project.
How to define a basic custom error type
The easiest way is to define a structure type and implement Error() string method, so that it satisfies the error interface.
type MyError struct {
Msg string
}
func (e MyError) Error() string {
return e.Msg
}When using it, you can return it like this:
func doSomething() error {
return MyError{Msg: "something went wrong"}
}This method is suitable for situations where you only need to wrap an error message. However, if you want to carry more information, such as error codes or operation types, you can continue to expand the structure field.
Add more context information: error code, operation name, etc.
Sometimes it is not enough to just look at the error message, and you also want to know which module the error belongs to and what the corresponding error code is. At this time, you can add some fields to the structure:
type AppError struct {
Code int
Op string
Message string
}
func (e AppError) Error() string {
return fmt.Sprintf("[%d] %s: %s", e.Code, e.Op, e.Message)
}Example of usage:
return AppError{
Code: 4001,
Op: "fetch_data",
Message: "invalid input",
}In this way, the source of the problem can be more clearly located in the log or interface return. And you can also judge the specific error type through type assertions and further process it.
Wrap the original error and keep the stack information (advanced usage)
If you want to not just record error information, but also track the call stack, you can combine fmt.Errorf and %w to wrap the original error, or use a third-party library such as pkg/errors .
However, starting from Go 1.13, the standard library has supported error wrapping and stack extraction:
if err := someFunc(); err != nil {
return fmt.Errorf("failed in myfunc: %w", err)
} Then you can use errors.Unwrap() or errors.As() to extract the original error. For example:
var target *MyError
if errors.As(err, &target) {
// Handle specific types of errors} If you want to include stack information in your custom errors, consider adding the stack []uintptr field in the structure, but this is usually used at the debugging tool or framework level, and general business code is not recommended to be overused.
Suggestions and precautions
- Keep it simple : Not every error requires a custom type, and it is enough to use
errors.Neworfmt.Errorfin simple scenarios. - Unified error structure : If the project is large in scale, it is recommended to unify error structure to facilitate unified processing and log output.
- Avoid duplicate wheels : Some projects may already have a wrong package library, first check if there are any ready-made ones available.
- Don't ignore error checking : even if you use a custom error, remember to check the return value.
Basically that's it. Although custom errors are not complicated in Go, if used properly, they can significantly improve code quality and troubleshooting efficiency.
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