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103 lines
4.3 KiB
103 lines
4.3 KiB
6 years ago
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// Copyright 2017 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package language implements BCP 47 language tags and related functionality.
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//
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// The most important function of package language is to match a list of
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// user-preferred languages to a list of supported languages.
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// It alleviates the developer of dealing with the complexity of this process
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// and provides the user with the best experience
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// (see https://blog.golang.org/matchlang).
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//
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//
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// Matching preferred against supported languages
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//
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// A Matcher for an application that supports English, Australian English,
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// Danish, and standard Mandarin can be created as follows:
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//
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// var matcher = language.NewMatcher([]language.Tag{
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// language.English, // The first language is used as fallback.
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// language.MustParse("en-AU"),
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// language.Danish,
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// language.Chinese,
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// })
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//
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// This list of supported languages is typically implied by the languages for
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// which there exists translations of the user interface.
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//
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// User-preferred languages usually come as a comma-separated list of BCP 47
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// language tags.
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// The MatchString finds best matches for such strings:
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//
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// handler(w http.ResponseWriter, r *http.Request) {
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// lang, _ := r.Cookie("lang")
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// accept := r.Header.Get("Accept-Language")
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// tag, _ := language.MatchStrings(matcher, lang.String(), accept)
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//
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// // tag should now be used for the initialization of any
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// // locale-specific service.
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// }
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//
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// The Matcher's Match method can be used to match Tags directly.
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//
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// Matchers are aware of the intricacies of equivalence between languages, such
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// as deprecated subtags, legacy tags, macro languages, mutual
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// intelligibility between scripts and languages, and transparently passing
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// BCP 47 user configuration.
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// For instance, it will know that a reader of Bokmål Danish can read Norwegian
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// and will know that Cantonese ("yue") is a good match for "zh-HK".
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//
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//
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// Using match results
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//
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// To guarantee a consistent user experience to the user it is important to
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// use the same language tag for the selection of any locale-specific services.
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// For example, it is utterly confusing to substitute spelled-out numbers
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// or dates in one language in text of another language.
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// More subtly confusing is using the wrong sorting order or casing
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// algorithm for a certain language.
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//
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// All the packages in x/text that provide locale-specific services
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// (e.g. collate, cases) should be initialized with the tag that was
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// obtained at the start of an interaction with the user.
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//
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// Note that Tag that is returned by Match and MatchString may differ from any
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// of the supported languages, as it may contain carried over settings from
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// the user tags.
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// This may be inconvenient when your application has some additional
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// locale-specific data for your supported languages.
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// Match and MatchString both return the index of the matched supported tag
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// to simplify associating such data with the matched tag.
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//
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//
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// Canonicalization
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//
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// If one uses the Matcher to compare languages one does not need to
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// worry about canonicalization.
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//
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// The meaning of a Tag varies per application. The language package
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// therefore delays canonicalization and preserves information as much
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// as possible. The Matcher, however, will always take into account that
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// two different tags may represent the same language.
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//
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// By default, only legacy and deprecated tags are converted into their
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// canonical equivalent. All other information is preserved. This approach makes
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// the confidence scores more accurate and allows matchers to distinguish
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// between variants that are otherwise lost.
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//
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// As a consequence, two tags that should be treated as identical according to
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// BCP 47 or CLDR, like "en-Latn" and "en", will be represented differently. The
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// Matcher handles such distinctions, though, and is aware of the
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// equivalence relations. The CanonType type can be used to alter the
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// canonicalization form.
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//
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// References
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//
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// BCP 47 - Tags for Identifying Languages http://tools.ietf.org/html/bcp47
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//
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package language // import "golang.org/x/text/language"
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// TODO: explanation on how to match languages for your own locale-specific
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// service.
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