On Thu, Apr 30, 2020 at 9:42 PM Miki Tebeka <miki.teb...@gmail.com> wrote:
>
> I'm trying to find an example where strings.EqualFold returns true but
> comparison of strings.ToLower fails.
> I've found this example (in Python):
>
> s1 = "der Fluß"
> s2 = "der Fluss"
>
> print('lower', s1.lower() == s2.lower())
> print('fold ', s1.casefold() == s2.casefold())
>
> Which prints False for lower and True for casefold.
>
> When I try the same in Go
> package main
>
> import (
> "fmt"
> "strings"
> )
>
> func main() {
>
> s1 := "der Fluß"
> s2 := "der Fluss"
>
> fmt.Println("lower", strings.ToLower(s1) == strings.ToLower(s2))
> fmt.Println("fold ", strings.EqualFold(s1, s2))
> }
>
> I get false for both ToLower and EqualFold.
>
> Shouldn't Unicode folding be the same across languages?
> Also, does anyone have an example I can show in Go where ToLower does not
> compare and EqualFold does?
strings.EqualFold uses Unicode case folding, not case mapping. Case
folding is only one-to-one character transformations. Converting "ss"
to "ß" is case mapping, and as such is not used by strings.EqualFold.
For that, you want the x/text/search package, as in
package main
import (
"fmt"
"golang.org/x/text/language"
"golang.org/x/text/search"
)
func main() {
m := search.New(language.German, search.Loose)
s1 := "der Fluß"
s2 := "der Fluss"
fmt.Println(m.EqualString(s1, s2))
}
That should print true.
An example where strings.EqualFold does not return the same result as
strings.ToLower(s1) == strings.ToLower(s2) is
s1 := "σς"
s2 := "ΣΣ"
strings.EqualFold will return true but comparing the ToLower of the
strings will return false. This is because there are two lower case
forms of Σ (depending on position in the word), but strings.ToLower
can of course only return one.
Ian
--
You received this message because you are subscribed to the Google Groups
"golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to golang-nuts+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/golang-nuts/CAOyqgcU47SM2foJdGFH6mspRpppOUugLG15R_0ZhOGp2fbO6FA%40mail.gmail.com.
