gohugoio/hugo · error

can't sort {type}

Error message

can't sort {type}

What it means

The `sort` function only handles arrays, slices, and maps. After the kind switch at sort.go:44, any other reflect.Kind (string, int, struct, bool, etc.) falls into the default branch and produces this error with the type name interpolated. Sorting a scalar or a single struct is not meaningful.

Source

Thrown at tpl/collections/sort.go:50

	if l == nil {
		return nil, errors.New("sequence must be provided")
	}

	seqv, isNil := hreflect.Indirect(reflect.ValueOf(l))
	if isNil {
		return nil, errors.New("can't iterate over a nil value")
	}

	ctxv := reflect.ValueOf(ctx)

	var sliceType reflect.Type
	switch seqv.Kind() {
	case reflect.Array, reflect.Slice:
		sliceType = seqv.Type()
	case reflect.Map:
		sliceType = reflect.SliceOf(seqv.Type().Elem())
	default:
		return nil, errors.New("can't sort " + reflect.ValueOf(l).Type().String())
	}

	collator := langs.GetCollator1(ns.deps.Conf.Language().(*langs.Language))

	// Create a list of pairs that will be used to do the sort
	p := pairList{Collator: collator, sortComp: ns.sortComp, SortAsc: true, SliceType: sliceType}
	p.Pairs = make([]pair, seqv.Len())

	var sortByField string
	for i, l := range args {
		dStr, err := cast.ToStringE(l)
		switch {
		case i == 0 && err != nil:
			sortByField = ""
		case i == 0 && err == nil:
			sortByField = dStr
		case i == 1 && err == nil && dStr == "desc":
			p.SortAsc = false

View on GitHub (pinned to 52c9bd7908)

Solutions

1. Pass a slice or array: `{{ sort .Pages }}`.
2. To sort by a field, pass the collection as the first arg and the field name as the second: `{{ sort .Pages "Title" }}`.
3. Verify the variable is a collection before calling sort.

Example fix

// before
{{ sort .Title }}
// after
{{ sort .Pages "Title" }}

func isSortable(v any) bool {
    if v == nil { return false }
    switch reflect.TypeOf(v).Kind() {
    case reflect.Slice, reflect.Array, reflect.Map: return true
    default: return false
    }
}

When it happens

Trigger: Calling sort on a non-iterable value: `{{ sort "hello" }}`, `{{ sort 42 }}`, `{{ sort .Title }}` (a string), or `{{ sort .Page }}` (a struct).

Common situations: A developer accidentally passes a single page object or a scalar field instead of a collection, e.g. `{{ sort .Pages.Title }}` (a string) rather than `{{ sort .Pages "Title" }}` (sort the slice by field).

Related errors

• sequence must be provided
• can't iterate over a nil value
• operator argument must be string type
• isset unable to use key of type %T as index
• type %T not supported

AI-assisted analysis of gohugoio/hugo@52c9bd7908 (2026-08-09). Data as JSON: /api/errors/9ddccbc8615278c7. Report an issue: GitHub.