Most idiomatic way to select elements from an array in Golang?
There is no one-liner as you have it in Ruby, but with a helper function you can make it almost as short.
Here's our helper function that loops over a slice, and selects and returns only the elements that meet a criteria captured by a function value:
func filter(ss []string, test func(string) bool) (ret []string) {
for _, s := range ss {
if test(s) {
ret = append(ret, s)
}
}
return
}
Using this helper function your task:
ss := []string{"foo_1", "asdf", "loooooooong", "nfoo_1", "foo_2"}
mytest := func(s string) bool { return !strings.HasPrefix(s, "foo_") && len(s) <= 7 }
s2 := filter(ss, mytest)
fmt.Println(s2)
Output (try it on the Go Playground):
[asdf nfoo_1]
Note:
If it is expected that many elements will be selected, it might be profitable to allocate a "big" ret
slice beforehand, and use simple assignment instead of the append()
. And before returning, slice the ret
to have a length equal to the number of selected elements.
Note #2:
In my example I chose a test()
function which tells if an element is to be returned. So I had to invert your "exclusion" condition. Obviously you may write the helper function to expect a tester function which tells what to exclude (and not what to include).
Have a look at robpike's filter library. This would allow you to do:
package main
import (
"fmt"
"strings"
"filter"
)
func isNoFoo7(a string) bool {
return ! strings.HasPrefix(a, "foo_") && len(a) <= 7
}
func main() {
a := []string{"test", "some_other_test", "foo_etc"}
result := Choose(a, isNoFoo7)
fmt.Println(result) // [test]
}
Interestingly enough the README.md by Rob:
I wanted to see how hard it was to implement this sort of thing in Go, with as nice an API as I could manage. It wasn't hard. Having written it a couple of years ago, I haven't had occasion to use it once. Instead, I just use "for" loops. You shouldn't use it either.
So the most idiomatic way according to Rob would be something like:
func main() {
a := []string{"test", "some_other_test", "foo_etc"}
nofoos := []string{}
for i := range a {
if(!strings.HasPrefix(a[i], "foo_") && len(a[i]) <= 7) {
nofoos = append(nofoos, a[i])
}
}
fmt.Println(nofoos) // [test]
}
This style is very similar, if not identical, to the approach any C-family language takes.