strings: Docs & Examples unclear about difference between ToTitle and ToUpper

[dionysius]

What version of Go are you using (go version)?

The current documentation on https://golang.org/pkg/strings/

Does this issue reproduce with the latest release?

Yes, using the examples inside the strings package documentation

What operating system and processor architecture are you using (go env)?

None providable

What did you do?

Copied strings.ToTitle example to strings.ToUpper and changed ToTitle() to ToUpper():

package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.ToUpper("her royal highness"))
	fmt.Println(strings.ToUpper("loud noises"))
	fmt.Println(strings.ToUpper("хлеб"))
}

What did you expect to see?

A difference in output.

What did you see instead?

Example ToTitle (unmodified) outputs:

HER ROYAL HIGHNESS
LOUD NOISES
ХЛЕБ

Example ToUpper (modified as described above) outputs:

HER ROYAL HIGHNESS
LOUD NOISES
ХЛЕБ

No difference. So for me it is unclear which function is now the correct one to use for an imaginary case.

[dionysius]

Or in other words:

package main

import (
	"fmt"
	"strings"
)

func main() {
	a := strings.ToTitle("her royal highness, loud noises, хлеб")
	b := strings.ToUpper("her royal highness, loud noises, хлеб")
	fmt.Println(a == b)
}

// outputs:
// true

Document an example that can help the user decide which function is the right one to use for his case. Something that helps him understand what the difference is.

[toothrot]

Title case and Upper case of a character have distinct definitions in unicode to allow for specific characters that have distinctive differences: https://unicode.org/faq/casemap_charprop.html#4

dz, in latin, is one for example: http://www.fileformat.info/info/unicode/char/01f3/index.htm

It's hard to find a good example to add that doesn't add confusion to people who aren't already familiar with this feature of unicode.

package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.ToUpper("dzz")) // DZZ
	fmt.Println(strings.ToTitle("dzz")) // DzZ
}

What would you suggest?

/cc @griesemer

[griesemer]

Assigned to @mpvl who is our local Unicode expert.

[dionysius]

It's hard to find a good example to add that doesn't add confusion to people who aren't already familiar with this feature of unicode.

True! After thinking about it for a short while I know what the difference means now as well. I thought, why not help and raise an small issue to make the difference a little more clear in the docs to be - in the future - quicker to decide what to use for a specific case.

I think just add a little ToTitle specific string for the ToTitle example and we're good to go.

If you want, I'm fine also with a decision against it.

[gopherbot]

Change https://golang.org/cl/224097 mentions this issue: strings: change examples for ToTitle and Title, fixes #37334

[fenollp]

Quoting https://unicode.org/faq/casemap_charprop.html#4 (@toothrot's link):

Titlecase is also used in forming a sentence by capitalizing the first word, and for forming proper names.
The titlecase mapping in the Unicode Standard is the mapping applied to the initial character in a word.

(emphasis mine)

To recap: strings.Title() (which mapped on words) is deprecated and replaced with strings.ToTitle() which maps on letters.
Why was it named ToTitle when it seems to not even match the Unicode description?

[ianlancetaylor]

strings.Title is not being replaced by strings.ToTitle. Those two functions do different things.