forked from elves/elvish
/
index_list.go
117 lines (107 loc) · 2.33 KB
/
index_list.go
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package vals
import (
"errors"
"strconv"
"strings"
"github.com/xiaq/persistent/vector"
)
var (
errIndexMustBeString = errors.New("index must be string")
errIndexMustBeNumber = errors.New("index or slice component must be number")
errIndexOutOfRange = errors.New("index out of range")
)
type listIndexable interface {
Lener
Index(int) (interface{}, bool)
SubVector(int, int) vector.Vector
}
var _ listIndexable = vector.Vector(nil)
func indexList(l listIndexable, rawIndex interface{}) (interface{}, error) {
index, err := ConvertListIndex(rawIndex, l.Len())
if err != nil {
return nil, err
}
if index.Slice {
return l.SubVector(index.Lower, index.Upper), nil
}
// Bounds are already checked.
value, _ := l.Index(index.Lower)
return value, nil
}
// ListIndex represents a (converted) list index.
type ListIndex struct {
Slice bool
Lower int
Upper int
}
// ConvertListIndex parses a list index, check whether it is valid, and returns
// the converted structure.
func ConvertListIndex(rawIndex interface{}, n int) (*ListIndex, error) {
s, ok := rawIndex.(string)
if !ok {
return nil, errIndexMustBeString
}
slice, i, j, err := parseListIndex(s, n)
if err != nil {
return nil, err
}
if i < 0 {
i += n
}
if j < 0 {
j += n
}
if slice {
if !(0 <= i && i <= j && j <= n) {
return nil, errIndexOutOfRange
}
} else {
if !(0 <= i && i < n) {
return nil, errIndexOutOfRange
}
}
return &ListIndex{slice, i, j}, nil
}
// ListIndex = Number |
// Number ':' Number
func parseListIndex(s string, n int) (slice bool, i int, j int, err error) {
colon := strings.IndexRune(s, ':')
if colon == -1 {
// A single number
i, err := atoi(s)
if err != nil {
return false, 0, 0, err
}
return false, i, 0, nil
}
if s[:colon] == "" {
i = 0
} else {
i, err = atoi(s[:colon])
if err != nil {
return false, 0, 0, err
}
}
if s[colon+1:] == "" {
j = n
} else {
j, err = atoi(s[colon+1:])
if err != nil {
return false, 0, 0, err
}
}
// Two numbers
return true, i, j, nil
}
// atoi is a wrapper around strconv.Atoi, converting strconv.ErrRange to
// errIndexOutOfRange.
func atoi(a string) (int, error) {
i, err := strconv.Atoi(a)
if err != nil {
if err.(*strconv.NumError).Err == strconv.ErrRange {
return 0, errIndexOutOfRange
}
return 0, errIndexMustBeNumber
}
return i, nil
}