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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package language
import (
// The Coverage interface is used to define the level of coverage of an
// internationalization service. Note that not all types are supported by all
// services. As lists may be generated on the fly, it is recommended that users
// of a Coverage cache the results.
type Coverage interface {
// Tags returns the list of supported tags.
Tags() []Tag
// BaseLanguages returns the list of supported base languages.
BaseLanguages() []Base
// Scripts returns the list of supported scripts.
Scripts() []Script
// Regions returns the list of supported regions.
Regions() []Region
var (
// Supported defines a Coverage that lists all supported subtags. Tags
// always returns nil.
Supported Coverage = allSubtags{}
// TODO:
// - Support Variants, numbering systems.
// - CLDR coverage levels.
// - Set of common tags defined in this package.
type allSubtags struct{}
// Regions returns the list of supported regions. As all regions are in a
// consecutive range, it simply returns a slice of numbers in increasing order.
// The "undefined" region is not returned.
func (s allSubtags) Regions() []Region {
reg := make([]Region, language.NumRegions)
for i := range reg {
reg[i] = Region{language.Region(i + 1)}
return reg
// Scripts returns the list of supported scripts. As all scripts are in a
// consecutive range, it simply returns a slice of numbers in increasing order.
// The "undefined" script is not returned.
func (s allSubtags) Scripts() []Script {
scr := make([]Script, language.NumScripts)
for i := range scr {
scr[i] = Script{language.Script(i + 1)}
return scr
// BaseLanguages returns the list of all supported base languages. It generates
// the list by traversing the internal structures.
func (s allSubtags) BaseLanguages() []Base {
bs := language.BaseLanguages()
base := make([]Base, len(bs))
for i, b := range bs {
base[i] = Base{b}
return base
// Tags always returns nil.
func (s allSubtags) Tags() []Tag {
return nil
// coverage is used used by NewCoverage which is used as a convenient way for
// creating Coverage implementations for partially defined data. Very often a
// package will only need to define a subset of slices. coverage provides a
// convenient way to do this. Moreover, packages using NewCoverage, instead of
// their own implementation, will not break if later new slice types are added.
type coverage struct {
tags func() []Tag
bases func() []Base
scripts func() []Script
regions func() []Region
func (s *coverage) Tags() []Tag {
if s.tags == nil {
return nil
return s.tags()
// bases implements sort.Interface and is used to sort base languages.
type bases []Base
func (b bases) Len() int {
return len(b)
func (b bases) Swap(i, j int) {
b[i], b[j] = b[j], b[i]
func (b bases) Less(i, j int) bool {
return b[i].langID < b[j].langID
// BaseLanguages returns the result from calling s.bases if it is specified or
// otherwise derives the set of supported base languages from tags.
func (s *coverage) BaseLanguages() []Base {
if s.bases == nil {
tags := s.Tags()
if len(tags) == 0 {
return nil
a := make([]Base, len(tags))
for i, t := range tags {
a[i] = Base{language.Language(t.tag.LangID)}
k := 0
for i := 1; i < len(a); i++ {
if a[k] != a[i] {
a[k] = a[i]
return a[:k+1]
return s.bases()
func (s *coverage) Scripts() []Script {
if s.scripts == nil {
return nil
return s.scripts()
func (s *coverage) Regions() []Region {
if s.regions == nil {
return nil
return s.regions()
// NewCoverage returns a Coverage for the given lists. It is typically used by
// packages providing internationalization services to define their level of
// coverage. A list may be of type []T or func() []T, where T is either Tag,
// Base, Script or Region. The returned Coverage derives the value for Bases
// from Tags if no func or slice for []Base is specified. For other unspecified
// types the returned Coverage will return nil for the respective methods.
func NewCoverage(list ...interface{}) Coverage {
s := &coverage{}
for _, x := range list {
switch v := x.(type) {
case func() []Base:
s.bases = v
case func() []Script:
s.scripts = v
case func() []Region:
s.regions = v
case func() []Tag:
s.tags = v
case []Base:
s.bases = func() []Base { return v }
case []Script:
s.scripts = func() []Script { return v }
case []Region:
s.regions = func() []Region { return v }
case []Tag:
s.tags = func() []Tag { return v }
panic(fmt.Sprintf("language: unsupported set type %T", v))
return s