163 lines
4.9 KiB
Go
163 lines
4.9 KiB
Go
// Copyright 2014 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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//go:generate go run gen.go gen_trieval.go
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// Package cases provides general and language-specific case mappers.
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package cases // import "golang.org/x/text/cases"
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import (
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"golang.org/x/text/language"
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"golang.org/x/text/transform"
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)
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// References:
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// - Unicode Reference Manual Chapter 3.13, 4.2, and 5.18.
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// - https://www.unicode.org/reports/tr29/
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// - https://www.unicode.org/Public/6.3.0/ucd/CaseFolding.txt
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// - https://www.unicode.org/Public/6.3.0/ucd/SpecialCasing.txt
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// - https://www.unicode.org/Public/6.3.0/ucd/DerivedCoreProperties.txt
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// - https://www.unicode.org/Public/6.3.0/ucd/auxiliary/WordBreakProperty.txt
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// - https://www.unicode.org/Public/6.3.0/ucd/auxiliary/WordBreakTest.txt
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// - http://userguide.icu-project.org/transforms/casemappings
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// TODO:
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// - Case folding
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// - Wide and Narrow?
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// - Segmenter option for title casing.
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// - ASCII fast paths
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// - Encode Soft-Dotted property within trie somehow.
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// A Caser transforms given input to a certain case. It implements
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// transform.Transformer.
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//
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// A Caser may be stateful and should therefore not be shared between
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// goroutines.
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type Caser struct {
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t transform.SpanningTransformer
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}
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// Bytes returns a new byte slice with the result of converting b to the case
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// form implemented by c.
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func (c Caser) Bytes(b []byte) []byte {
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b, _, _ = transform.Bytes(c.t, b)
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return b
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}
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// String returns a string with the result of transforming s to the case form
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// implemented by c.
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func (c Caser) String(s string) string {
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s, _, _ = transform.String(c.t, s)
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return s
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}
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// Reset resets the Caser to be reused for new input after a previous call to
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// Transform.
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func (c Caser) Reset() { c.t.Reset() }
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// Transform implements the transform.Transformer interface and transforms the
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// given input to the case form implemented by c.
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func (c Caser) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
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return c.t.Transform(dst, src, atEOF)
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}
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// Span implements the transform.SpanningTransformer interface.
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func (c Caser) Span(src []byte, atEOF bool) (n int, err error) {
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return c.t.Span(src, atEOF)
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}
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// Upper returns a Caser for language-specific uppercasing.
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func Upper(t language.Tag, opts ...Option) Caser {
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return Caser{makeUpper(t, getOpts(opts...))}
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}
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// Lower returns a Caser for language-specific lowercasing.
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func Lower(t language.Tag, opts ...Option) Caser {
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return Caser{makeLower(t, getOpts(opts...))}
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}
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// Title returns a Caser for language-specific title casing. It uses an
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// approximation of the default Unicode Word Break algorithm.
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func Title(t language.Tag, opts ...Option) Caser {
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return Caser{makeTitle(t, getOpts(opts...))}
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}
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// Fold returns a Caser that implements Unicode case folding. The returned Caser
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// is stateless and safe to use concurrently by multiple goroutines.
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//
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// Case folding does not normalize the input and may not preserve a normal form.
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// Use the collate or search package for more convenient and linguistically
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// sound comparisons. Use golang.org/x/text/secure/precis for string comparisons
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// where security aspects are a concern.
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func Fold(opts ...Option) Caser {
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return Caser{makeFold(getOpts(opts...))}
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}
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// An Option is used to modify the behavior of a Caser.
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type Option func(o options) options
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// TODO: consider these options to take a boolean as well, like FinalSigma.
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// The advantage of using this approach is that other providers of a lower-case
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// algorithm could set different defaults by prefixing a user-provided slice
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// of options with their own. This is handy, for instance, for the precis
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// package which would override the default to not handle the Greek final sigma.
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var (
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// NoLower disables the lowercasing of non-leading letters for a title
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// caser.
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NoLower Option = noLower
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// Compact omits mappings in case folding for characters that would grow the
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// input. (Unimplemented.)
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Compact Option = compact
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)
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// TODO: option to preserve a normal form, if applicable?
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type options struct {
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noLower bool
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simple bool
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// TODO: segmenter, max ignorable, alternative versions, etc.
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ignoreFinalSigma bool
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}
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func getOpts(o ...Option) (res options) {
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for _, f := range o {
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res = f(res)
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}
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return
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}
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func noLower(o options) options {
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o.noLower = true
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return o
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}
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func compact(o options) options {
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o.simple = true
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return o
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}
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// HandleFinalSigma specifies whether the special handling of Greek final sigma
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// should be enabled. Unicode prescribes handling the Greek final sigma for all
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// locales, but standards like IDNA and PRECIS override this default.
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func HandleFinalSigma(enable bool) Option {
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if enable {
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return handleFinalSigma
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}
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return ignoreFinalSigma
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}
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func ignoreFinalSigma(o options) options {
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o.ignoreFinalSigma = true
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return o
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}
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func handleFinalSigma(o options) options {
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o.ignoreFinalSigma = false
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return o
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}
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