Thanks!
On Friday, May 1, 2020 at 8:21:48 AM UTC+3, Ian Lance Taylor wrote:
>
> On Thu, Apr 30, 2020 at 9:42 PM Miki Tebeka <miki....@gmail.com
> <javascript:>> 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
>
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