1 // Copyright 2017 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4 5 // Package language implements BCP 47 language tags and related functionality.
6 //
7 // The most important function of package language is to match a list of
8 // user-preferred languages to a list of supported languages.
9 // It alleviates the developer of dealing with the complexity of this process
10 // and provides the user with the best experience
11 // (see https://blog.golang.org/matchlang).
12 //
13 // # Matching preferred against supported languages
14 //
15 // A Matcher for an application that supports English, Australian English,
16 // Danish, and standard Mandarin can be created as follows:
17 //
18 // var matcher = language.NewMatcher([]language.Tag{
19 // language.English, // The first language is used as fallback.
20 // language.MustParse("en-AU"),
21 // language.Danish,
22 // language.Chinese,
23 // })
24 //
25 // This list of supported languages is typically implied by the languages for
26 // which there exists translations of the user interface.
27 //
28 // User-preferred languages usually come as a comma-separated list of BCP 47
29 // language tags.
30 // The MatchString finds best matches for such strings:
31 //
32 // handler(w http.ResponseWriter, r *http.Request) {
33 // lang, _ := r.Cookie("lang")
34 // accept := r.Header.Get("Accept-Language")
35 // tag, _ := language.MatchStrings(matcher, lang.String(), accept)
36 //
37 // // tag should now be used for the initialization of any
38 // // locale-specific service.
39 // }
40 //
41 // The Matcher's Match method can be used to match Tags directly.
42 //
43 // Matchers are aware of the intricacies of equivalence between languages, such
44 // as deprecated subtags, legacy tags, macro languages, mutual
45 // intelligibility between scripts and languages, and transparently passing
46 // BCP 47 user configuration.
47 // For instance, it will know that a reader of Bokmål Danish can read Norwegian
48 // and will know that Cantonese ("yue") is a good match for "zh-HK".
49 //
50 // # Using match results
51 //
52 // To guarantee a consistent user experience to the user it is important to
53 // use the same language tag for the selection of any locale-specific services.
54 // For example, it is utterly confusing to substitute spelled-out numbers
55 // or dates in one language in text of another language.
56 // More subtly confusing is using the wrong sorting order or casing
57 // algorithm for a certain language.
58 //
59 // All the packages in x/text that provide locale-specific services
60 // (e.g. collate, cases) should be initialized with the tag that was
61 // obtained at the start of an interaction with the user.
62 //
63 // Note that Tag that is returned by Match and MatchString may differ from any
64 // of the supported languages, as it may contain carried over settings from
65 // the user tags.
66 // This may be inconvenient when your application has some additional
67 // locale-specific data for your supported languages.
68 // Match and MatchString both return the index of the matched supported tag
69 // to simplify associating such data with the matched tag.
70 //
71 // # Canonicalization
72 //
73 // If one uses the Matcher to compare languages one does not need to
74 // worry about canonicalization.
75 //
76 // The meaning of a Tag varies per application. The language package
77 // therefore delays canonicalization and preserves information as much
78 // as possible. The Matcher, however, will always take into account that
79 // two different tags may represent the same language.
80 //
81 // By default, only legacy and deprecated tags are converted into their
82 // canonical equivalent. All other information is preserved. This approach makes
83 // the confidence scores more accurate and allows matchers to distinguish
84 // between variants that are otherwise lost.
85 //
86 // As a consequence, two tags that should be treated as identical according to
87 // BCP 47 or CLDR, like "en-Latn" and "en", will be represented differently. The
88 // Matcher handles such distinctions, though, and is aware of the
89 // equivalence relations. The CanonType type can be used to alter the
90 // canonicalization form.
91 //
92 // # References
93 //
94 // BCP 47 - Tags for Identifying Languages http://tools.ietf.org/html/bcp47
95 package language // import "golang.org/x/text/language"
96 97 // TODO: explanation on how to match languages for your own locale-specific
98 // service.
99