Golang errors: Difference between revisions
From wikinotes
Line 30: | Line 30: | ||
</blockquote><!-- Error Objects --> | </blockquote><!-- Error Objects --> | ||
== Error | == Error Types == | ||
<blockquote> | <blockquote> | ||
Errors are often pre-defined as constants | |||
<syntaxhighlight lang="go"> | |||
require "errors" | |||
var UserNotExistError = errors.New("User does not exist") | |||
func DoAs(user string) error { | |||
// ... | |||
return UserNotExistError | |||
} | |||
</syntaxhighlight> | |||
</blockquote><!-- Error Verification --> | </blockquote><!-- Error Verification --> | ||
</blockquote><!-- Errors --> | </blockquote><!-- Errors --> |
Revision as of 13:04, 18 June 2022
Go seems to discourage the use of exception-style control-flows,
encouraging the use of errors in return-values instead.
Errors
Error Objects
Go prefers passing error objects as return values to exceptions.
Errors can be any object that expose theError() string
method.require "errors" require "fmt" // build ad-hoc error fmt.Errorf("User does not exist") errors.New("User does not exist")Functions generally return an error as the last value on fail,
or nil on successfunc doThing (value int, error) { if success { return 123, nil // success } return 0, fmt.Errorf("User does not exist") // fail }Error Types
Errors are often pre-defined as constants
require "errors" var UserNotExistError = errors.New("User does not exist") func DoAs(user string) error { // ... return UserNotExistError }
Panic
panic
A
panic
is go's repacement for exceptions.
If a panic is not caught, it bubbles to the top of the application, and it exits with an error.panic("I encountered an error")recover
You can check the value of a panic (if one has been raised) using
recover()
.panic("I encountered an error") // raise a panic err := recover() // returns nil/error-msg-if-presentIt is common to handle panics in deferred functions
func main() { fmt.Println("hi") panic("I just encountered an error") defer func() { if err := recover(); err != nil { fmt.Println("Error: ", err) panic(err) // <<-- re-raise panic } } fmt.Println("bye") // <-- never runs }