github.com/hectorj/go-resultgen
A go:generate tool to generate some kind of result types (except it isn't generic nor monadic).
The generated type exposes this interface:
type MyTypeResult interface {
// GetError tells us if the result is an error or not (in which case it returns `nil`).
GetError() error
// GetMyType gives us the encapsulated result value. Panics if the result is actually an error.
GetMyType() MyType
}It helps ensure a type cannot be in an invalid state, and is semantically more correct than a double return. I also think it is nicer to read, but that is very subjective.
The traditional Go way:
// you don't want to return something AND an error.
// you actually want to return something OR an error.
func buildSomething(someParam interface{}) (something, error) {
if someParam == nil {
return something{}, errors.New("someParam should not be nil")
}
return something{
param: someParam,
}, nil
}
func main() {
smthing, err := buildSomething(nil)
if err != nil {
// We did check the error, so the errcheck linter won't complain
log.Println(err)
}
// But we did not return! We still have our `something`, but in an invalid state.
smthing.SomeMethod()
}With a Result type:
func buildSomething(someParam interface{}) somethingResult {
if someParam == nil {
return NewFailedSomethingResult(errors.New("someParam should not be nil"))
}
return NewValidSomethingResult(something{
param: someParam,
})
}
func main() {
smthingResult := buildSomething(nil)
if err := smthingResult.GetError(); err != nil {
log.Println(err)
}
// Here, if there was an error, we will immediately panic.
// This way, at no point in time did the user have an invalid `something`.
smthing := smthingResult.GetSomething()
smthing.SomeMethod()
}Installation
go get -u github.com/hectorj/go-resultgen
Usage
It is meant to be used with the go generate command.
See the example.
There is also a "strict" mode, that will panic immediately if you try to get the value without checking the error at least once. I recommend it when running your tests. See this other example.