I am parsing a form and have written a number of functions func parseAndValidateX(val string) (T, err) where T is any type.
Now I would like to write a closure func catchError(T, Error) T, so that I can do something like:
errors []Error
func catchError(val T, err Error) T {
if err != nil {
//append err to errors
}
return val
}
data = MyStruct {
Age = catchError(parseAndValidateAge("5")) // Age is a int
DistanceFromHome = catchError(parseAndValidatePi("3.14")) // DistanceFromHome is a float
Location = catchError(parseAndValidatePi("3.14,2.0")) //Location is a custom Struct
}
if len(errors) > 0 {
// o, oh
}
Is this possible in Go? How can this be done easily/idiomatically?
Nope; you cannot do that since Go has no parametric polymorphism for user-defined functions. All you can do is take and return interface{} and add type assertions at the call sites.
Everything in Go is type-safe if you don't use the unsafe package, so you don't have to worry about that. A type assertion will fail at runtime instead of at compile-time, though.
If you are willing to violate DRY, though:
type errorList []Error
func (l *errorList) addIfNotNil(err Error) {
if err != nil {
*l = append(*l, err)
}
}
func (l *errorList) int(x int, err Error) int {
l.addIfNotNil(err)
return x
}
func (l *errorList) float32(x float32, err Error) float32 {
l.addIfNotNil(err)
return x
}
list := errorList([]Error{})
data := MyStruct{
Age: list.int(parseAndValidateAge("5")),
DistanceFromHome: list.float32(parseAndValidatePi("3.14")),
}