How are errors handled in Go? What is the difference between errors.Is and errors.As?

In Go, errors are handled through the return value of type error. Usually, a function returns a result and an error, and the calling code checks whether the error is nil to determine if an error occurred.

The errors package from the standard library provides functions for working with errors:

• errors.Is(err, target error) bool — checks whether err or any error in its chain of wrappers matches the target error. It is used for comparing errors by value, even if the error is wrapped.

• errors.As(err, target interface{}) bool — attempts to assign err or one of the errors in its chain to the type specified in target (a pointer to an interface or struct). If successful, it assigns the error to target and returns true. It is used for extracting a specific error type from the chain.

Example:

if errors.Is(err, sql.ErrNoRows) {
    // Handle case when record is not found
}

var pathErr *os.PathError
if errors.As(err, &pathErr) {
    // Handle specific os.PathError error
}