wailsapp/wails · error

Values for %T isn't a slice

Error message

Values for %T isn't a slice

What it means

TypeScriptify.AddEnum panics when the value passed via AddEnum(values interface{}) is not a reflect.Slice. The method uses reflection over an untyped interface{}, so a non-slice argument (a map, array is fine as slice-kind? no—only slice kind passes, arrays have Kind Array) cannot be iterated as enum elements.

Source

Thrown at v2/internal/typescriptify/typescriptify.go:346

		}
	}
	t.fields = append(t.fields, fmt.Sprintf("%s%s: Record<%s, %s>;", t.indent, fieldName, keyTypeStr, valueTypePrefix+valueTypeName+valueTypeSuffix))
	if valueType.Kind() == reflect.Struct {
		t.constructorBody = append(t.constructorBody, fmt.Sprintf("%s%sthis%s = this.convertValues(source[\"%s\"], %s, true);",
			t.indent, t.indent, dotField, strippedFieldName, t.prefix+valueTypePrefix+valueTypeName+valueTypeSuffix+t.suffix))
	} else {
		t.constructorBody = append(t.constructorBody, fmt.Sprintf("%s%sthis%s = source[\"%s\"];",
			t.indent, t.indent, dotField, strippedFieldName))
	}
}

func (t *TypeScriptify) AddEnum(values interface{}) *TypeScriptify {
	if t.enums == nil {
		t.enums = map[reflect.Type][]enumElement{}
	}
	items := reflect.ValueOf(values)
	if items.Kind() != reflect.Slice {
		panic(fmt.Sprintf("Values for %T isn't a slice", values))
	}

	var elements []enumElement
	for i := 0; i < items.Len(); i++ {
		item := items.Index(i)

		var el enumElement
		if item.Kind() == reflect.Struct {
			r := reflector.New(item.Interface())
			val, err := r.Field("Value").Get()
			if err != nil {
				panic(fmt.Sprint("missing Type field in ", item.Type().String()))
			}
			name, err := r.Field("TSName").Get()
			if err != nil {
				panic(fmt.Sprint("missing TSName field in ", item.Type().String()))
			}
			el.value = val

View on GitHub (pinned to 0e754b1b40)

Solutions

1. Pass a slice: []MyEnum{...} rather than an array, map, or single value
2. If the value arrives dynamically, check reflect.ValueOf(v).Kind() == reflect.Slice before calling AddEnum

Example fix

// before
ts.AddEnum(MyEnum{})         // struct: panics
ts.AddEnum([3]MyEnum{})      // array: panics

// after
ts.AddEnum([]MyEnum{A, B, C})

if reflect.ValueOf(values).Kind() != reflect.Slice {
    return fmt.Errorf("AddEnum needs a slice, got %T", values)
}
ts.AddEnum(values)

func addEnumSlice[T any](t *typescriptify.TypeScriptify, values []T) {
    // []T is always Slice kind; misuse becomes a compile error
    t.AddEnum(values)
}

When it happens

Trigger: Calling AddEnum with a single value, a map, an array ([N]T has Kind Array, not Slice), or a pointer to a slice instead of a slice.

Common situations: Extending the wails binding generator with custom enums and passing e.g. an enum map[string]int, one struct value, or a [3]MyEnum array instead of []MyEnum.

Related errors

• missing Type field in
• missing TSName field in
• has no TSName method
• binding method ID registration expects a function, got %s
• use ShowAndGetResults for open multiple files dialog

AI-assisted analysis of wailsapp/wails@0e754b1b40 (2026-08-15). Data as JSON: /api/errors/6ce8910e232dcd52. Report an issue: GitHub.