github.com/xyproto/u-root@v6.0.1-0.20200302025726-5528e0c77a3c+incompatible/cmds/core/elvish/eval/vals/index_string.go (about)

     1  package vals
     2  
     3  import (
     4  	"errors"
     5  	"unicode/utf8"
     6  )
     7  
     8  var errIndexNotAtRuneBoundary = errors.New("index not at rune boundary")
     9  
    10  func indexString(s string, index interface{}) (string, error) {
    11  	i, j, err := convertStringIndex(index, s)
    12  	if err != nil {
    13  		return "", err
    14  	}
    15  	return s[i:j], nil
    16  }
    17  
    18  func convertStringIndex(rawIndex interface{}, s string) (int, int, error) {
    19  	index, err := ConvertListIndex(rawIndex, len(s))
    20  	if err != nil {
    21  		return 0, 0, err
    22  	}
    23  	r, size := utf8.DecodeRuneInString(s[index.Lower:])
    24  	if r == utf8.RuneError {
    25  		return 0, 0, errIndexNotAtRuneBoundary
    26  	}
    27  	if index.Slice {
    28  		if r, _ := utf8.DecodeLastRuneInString(s[:index.Upper]); r == utf8.RuneError {
    29  			return 0, 0, errIndexNotAtRuneBoundary
    30  		}
    31  		return index.Lower, index.Upper, nil
    32  	}
    33  	return index.Lower, index.Lower + size, nil
    34  }