Golang errors: Difference between revisions
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</syntaxhighlight> | </syntaxhighlight> | ||
</blockquote><!-- Returning Errors --> | </blockquote><!-- Returning Errors --> | ||
== Wrapping Errors == | |||
<blockquote> | |||
</blockquote><!-- Wrapping Errors --> | |||
== Handling Errors == | |||
<blockquote> | |||
<syntaxhighlight lang="go"> | |||
func doThing { | |||
var err error | |||
if err = doThingOne; err != nil { | |||
if errors.Is(err, SomePreDefinedError) {...} | |||
if errors.As(err, SomeWrappedError) {...} | |||
} | |||
} | |||
</syntaxhighlight> | |||
</blockquote><!-- Handling Errors --> | |||
== Error Types == | == Error Types == |
Revision as of 14:04, 18 June 2022
Go seems to discourage the use of exception-style control-flows,
encouraging the use of errors in return-values instead.
Errors
Returning Errors
Go prefers passing error objects as return values to panicking (go's exception-like behaviour).
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 }Wrapping Errors
Handling Errors
func doThing { var err error if err = doThingOne; err != nil { if errors.Is(err, SomePreDefinedError) {...} if errors.As(err, SomeWrappedError) {...} } }Error Types
Errors are often pre-defined as package constants
require "errors" var UserNotExistError = errors.New("User does not exist") func DoAs(user string) error { return UserNotExistError }You can then check for a specific error
require "errors" err := DoAs("someuser") if errors.Is(err) {...}
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 }