What is the "idiomatic" version of this function? - go

Question

Trying to understand the mentality of Go. I wrote the following function which looks for *.txt files of a folder that have a date in the filename, get the latest date and return that date.
func getLatestDate(path string) (time.Time, error) {
if fns, e := filepath.Glob(filepath.Join(path, "*.txt")); e == nil {
re, _ := regexp.Compile(`_([0-9]{8}).txt$`)
max := ""
for _, fn := range fns {
if ms := re.FindStringSubmatch(fn); ms != nil {
if ms[1] > max {
max = ms[1]
}
}
}
date, _ := time.Parse("20060102", max)
return date, nil
} else {
return time.Time{}, e
}
}
What would be the more idiomatic version of this function, if there is one?

Answer 1

Here is my take
Use MustCompile to compile a static regexp. This will panic if it doesn't compile and saves an error check
Hoist compiling the regexp out of the function - you only need it compiled once. Note that I've called it with a lowercase initial letter so it won't be visible outside the package.
Use an early return when checking errors - this saves indentation and is idiomatic go
Use named return parameters for those early returns - saves defining nil values for types and typing in general (not to everyone's taste though)
return time.Parse directly which checks the errors (you weren't before)
The code
var dateRe = regexp.MustCompile(`_([0-9]{8}).txt$`)
func getLatestDate(path string) (date time.Time, err error) {
fns, err := filepath.Glob(filepath.Join(path, "*.txt"))
if err != nil {
return
}
max := ""
for _, fn := range fns {
if ms := dateRe.FindStringSubmatch(fn); ms != nil {
if ms[1] > max {
max = ms[1]
}
}
}
return time.Parse("20060102", max)
}

Answer 2

Here's how I would have written it. Don't ignore errors, use guard clauses for error handling, and don't recompile regexps inside a loop.
var datePat = regexp.MustCompile(`_([0-9]{8}).txt$`)
func getLatestDate(path string) (time.Time, error) {
fns, err := filepath.Glob(filepath.Join(path, "*.txt"))
if err != nil {
return time.Time{}, err
}
max := time.Time{}
for _, fn := range fns {
if ms := re.FindStringSubmatch(fn); ms != nil {
if t, err := time.Parse("20060102", ms[1]); err == nil && t.After(max) {
max = t
}
}
}
return max, nil
}