ntool/nstr/runes.go

package nstr

import "unicode"

// RuneIsLower checks if a character is lower case ('a' to 'z')
func RuneIsLower(c rune) bool {
	return 'a' <= c && c <= 'z'
}

// RuneToLower converts a character  'A' to 'Z' to its lower case
func RuneToLower(r rune) rune {
	if r >= 'A' && r <= 'Z' {
		return r + 32
	}
	return r
}

// RuneToLowerAll converts a character  'A' to 'Z' to its lower case
func RuneToLowerAll(rs []rune) []rune {
	for i := range rs {
		rs[i] = RuneToLower(rs[i])
	}
	return rs
}

// RuneIsUpper checks if a character is upper case ('A' to 'Z')
func RuneIsUpper(c rune) bool {
	return 'A' <= c && c <= 'Z'
}

// RuneToUpper converts a character  'a' to 'z' to its upper case
func RuneToUpper(r rune) rune {
	if r >= 'a' && r <= 'z' {
		return r - 32
	}
	return r
}

// RuneToUpperAll converts a character  'a' to 'z' to its upper case
func RuneToUpperAll(rs []rune) []rune {
	for i := range rs {
		rs[i] = RuneToUpper(rs[i])
	}
	return rs
}

// RuneIsDigit checks if a character is digit ('0' to '9')
func RuneIsDigit(r rune) bool {
	return r >= '0' && r <= '9'
}

// RuneIsLetter checks r is a letter but not CJK character.
func RuneIsLetter(r rune) bool {
	if !unicode.IsLetter(r) {
		return false
	}

	switch {
	// cjk char: /[\u3040-\u30ff\u3400-\u4dbf\u4e00-\u9fff\uf900-\ufaff\uff66-\uff9f]/
	// hiragana and katakana (Japanese only)
	case r >= '\u3034' && r < '\u30ff':
		return false
	// CJK unified ideographs extension A (Chinese, Japanese, and Korean)
	case r >= '\u3400' && r < '\u4dbf':
		return false
	// CJK unified ideographs (Chinese, Japanese, and Korean)
	case r >= '\u4e00' && r < '\u9fff':
		return false
	// CJK compatibility ideographs (Chinese, Japanese, and Korean)
	case r >= '\uf900' && r < '\ufaff':
		return false
	// half-width katakana (Japanese only)
	case r >= '\uff66' && r < '\uff9f':
		return false
	}

	return true
}