How to return a blank rune

Question

I'm looking at the string.Map function which must take a mapping function which returns a rune. I would like to eliminate runes that resolves false with a call to: unicode.IsPrint()

func Map(mapping func(rune) rune, s string) string

My function looks something like this:

func main() { 
func CleanUp(s string) string {

    clean := func(r rune) rune {
        if unicode.IsPrint(r) || r == rune('\n') {
            return r
        }
        return rune('')
    }

strings.Map(clean, s)
}

It should clean something like this "helloworld ' \x10" to "helloworld ' "

But rune('') is invalid. How can I return a blank or empty rune?

Try declaring a rune, not giving it a value and returning it https://golang.org/doc/go1#rune — Ullaakut, Sep 04 '18 at 21:17
Tried this already: `missing argument to conversion to rune: rune()` — user398520, Sep 04 '18 at 21:19

score 6 · Accepted Answer · answered Sep 04 '18 at 21:35

If you want to eliminate runes, a "blank rune" is not the way to go. That would not eliminate anything.

Assuming you're talking about strings.Map, the docs say

If mapping returns a negative value, the character is dropped from the string with no replacement.

Have your mapper return a negative value to indicate that a rune should be discarded.

score 5 · Answer 2 · answered Sep 04 '18 at 21:30

5

From what I understand, a rune is actually an integer value mapped to a unicode character, so this piece of code actually returns the \0 character if the condition check fails:

package main

import (
    "fmt"
    "strings"
    "unicode"
)

func main() {
    fmt.Println(CleanUp("helloworld ' \x10"))
}

func CleanUp(s string) string {

    clean := func(r rune) rune {
        if unicode.IsPrint(r) || r == rune('\n') {
            return r
        }
        return rune(0)
    }

    return strings.Map(clean, s)
}

Outputs

helloworld '

answered Sep 04 '18 at 21:30

Ullaakut

3,554
2
19
34

1

I see this in my test: expected: "hello ' " actual : "hello ' \x00" – user398520 Sep 04 '18 at 21:37
Try it here: https://play.golang.org/p/UNH02IuXQJL Works for me with your `yo` example – Ullaakut Sep 04 '18 at 21:37
I used the playground but my test shows a different result including \x00, rune(-1) works – user398520 Sep 04 '18 at 21:39
1

rune(0) part is what I was looking for to create a blank rune – Sumer Mar 03 '22 at 06:00

score 0 · Answer 3 · answered Jul 05 '21 at 03:09

Here is an example using the negative return value:

package main

import (
   "strings"
   "unicode"
)

func clean(r rune) rune {
   if r == '\n' || unicode.IsPrint(r) {
      return r
   }
   return -1
}

func main() { 
   s := strings.Map(clean, "helloworld ' \x10")
   println(s == "helloworld ' ")
}

How to return a blank rune

3 Answers3