зеркало из https://github.com/github/ruby.git
[ruby/strscan] Doc for StringScanner
(https://github.com/ruby/strscan/pull/96) #peek_byte and #scan_byte not updated (not available in my repo -- sorry). --------- https://github.com/ruby/strscan/commit/0123da7352 Co-authored-by: Sutou Kouhei <kou@cozmixng.org>
This commit is contained in:
Burdette Lamar
Hiroshi SHIBATA
Родитель
5611e249e1
Коммит
974ed1408c
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## Helper Methods
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These helper methods display values returned by scanner's methods.
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### `put_situation(scanner)`
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Display scanner's situation:
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- Byte position (`#pos`).
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- Character position (`#charpos`)
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- Target string (`#rest`) and size (`#rest_size`).
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```
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scanner = StringScanner.new('foobarbaz')
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scanner.scan(/foo/)
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put_situation(scanner)
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# Situation:
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# pos: 3
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# charpos: 3
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# rest: "barbaz"
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# rest_size: 6
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```
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### `put_match_values(scanner)`
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Display the scanner's match values:
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```
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scanner = StringScanner.new('Fri Dec 12 1975 14:39')
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pattern = /(?<wday>\w+) (?<month>\w+) (?<day>\d+) /
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scanner.match?(pattern)
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put_match_values(scanner)
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# Basic match values:
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# matched?: true
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# matched_size: 11
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# pre_match: ""
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# matched : "Fri Dec 12 "
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# post_match: "1975 14:39"
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# Captured match values:
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# size: 4
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# captures: ["Fri", "Dec", "12"]
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# named_captures: {"wday"=>"Fri", "month"=>"Dec", "day"=>"12"}
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# values_at: ["Fri Dec 12 ", "Fri", "Dec", "12", nil]
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# []:
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# [0]: "Fri Dec 12 "
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# [1]: "Fri"
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# [2]: "Dec"
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# [3]: "12"
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# [4]: nil
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```
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### `match_values_cleared?(scanner)`
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Returns whether the scanner's match values are all properly cleared:
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```
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scanner = StringScanner.new('foobarbaz')
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match_values_cleared?(scanner) # => true
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put_match_values(scanner)
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# Basic match values:
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# matched?: false
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# matched_size: nil
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# pre_match: nil
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# matched : nil
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# post_match: nil
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# Captured match values:
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# size: nil
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# captures: nil
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# named_captures: {}
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# values_at: nil
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# [0]: nil
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scanner.scan(/foo/)
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match_values_cleared?(scanner) # => false
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```
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## The Code
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```
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def put_situation(scanner)
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puts '# Situation:'
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puts "# pos: #{scanner.pos}"
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puts "# charpos: #{scanner.charpos}"
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puts "# rest: #{scanner.rest.inspect}"
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puts "# rest_size: #{scanner.rest_size}"
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end
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```
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```
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def put_match_values(scanner)
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puts '# Basic match values:'
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puts "# matched?: #{scanner.matched?}"
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value = scanner.matched_size || 'nil'
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puts "# matched_size: #{value}"
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puts "# pre_match: #{scanner.pre_match.inspect}"
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puts "# matched : #{scanner.matched.inspect}"
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puts "# post_match: #{scanner.post_match.inspect}"
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puts '# Captured match values:'
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puts "# size: #{scanner.size}"
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puts "# captures: #{scanner.captures}"
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puts "# named_captures: #{scanner.named_captures}"
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if scanner.size.nil?
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puts "# values_at: #{scanner.values_at(0)}"
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puts "# [0]: #{scanner[0]}"
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else
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puts "# values_at: #{scanner.values_at(*(0..scanner.size))}"
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puts "# []:"
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scanner.size.times do |i|
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puts "# [#{i}]: #{scanner[i].inspect}"
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end
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end
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end
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```
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```
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def match_values_cleared?(scanner)
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scanner.matched? == false &&
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scanner.matched_size.nil? &&
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scanner.matched.nil? &&
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scanner.pre_match.nil? &&
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scanner.post_match.nil? &&
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scanner.size.nil? &&
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scanner[0].nil? &&
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scanner.captures.nil? &&
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scanner.values_at(0..1).nil? &&
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scanner.named_captures == {}
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end
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```
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[1]: rdoc-ref:StringScanner@Stored+String
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[2]: rdoc-ref:StringScanner@Byte+Position+-28Position-29
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[3]: rdoc-ref:StringScanner@Target+Substring
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[4]: rdoc-ref:StringScanner@Setting+the+Target+Substring
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[5]: rdoc-ref:StringScanner@Traversing+the+Target+Substring
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[6]: https://docs.ruby-lang.org/en/master/Regexp.html
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[7]: rdoc-ref:StringScanner@Character+Position
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[8]: https://docs.ruby-lang.org/en/master/String.html#method-i-5B-5D
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[9]: rdoc-ref:StringScanner@Match+Values
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[10]: rdoc-ref:StringScanner@Fixed-Anchor+Property
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[11]: rdoc-ref:StringScanner@Positions
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[13]: rdoc-ref:StringScanner@Captured+Match+Values
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[14]: rdoc-ref:StringScanner@Querying+the+Target+Substring
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[15]: rdoc-ref:StringScanner@Searching+the+Target+Substring
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[16]: https://docs.ruby-lang.org/en/master/Regexp.html#class-Regexp-label-Groups+and+Captures
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[17]: rdoc-ref:StringScanner@Matching
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[18]: rdoc-ref:StringScanner@Basic+Match+Values
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\Class `StringScanner` supports processing a stored string as a stream;
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this code creates a new `StringScanner` object with string `'foobarbaz'`:
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```
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require 'strscan'
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scanner = StringScanner.new('foobarbaz')
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```
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## About the Examples
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All examples here assume that `StringScanner` has been required:
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```
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require 'strscan'
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```
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Some examples here assume that these constants are defined:
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```
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MULTILINE_TEXT = <<~EOT
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Go placidly amid the noise and haste,
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and remember what peace there may be in silence.
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EOT
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HIRAGANA_TEXT = 'こんにちは'
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ENGLISH_TEXT = 'Hello'
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```
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Some examples here assume that certain helper methods are defined:
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- `put_situation(scanner)`:
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Displays the values of the scanner's
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methods #pos, #charpos, #rest, and #rest_size.
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- `put_match_values(scanner)`:
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Displays the scanner's [match values][9].
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- `match_values_cleared?(scanner)`:
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Returns whether the scanner's [match values][9] are cleared.
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See examples [here][ext/strscan/helper_methods_md.html].
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## The `StringScanner` \Object
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This code creates a `StringScanner` object
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(we'll call it simply a _scanner_),
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and shows some of its basic properties:
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```
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scanner = StringScanner.new('foobarbaz')
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scanner.string # => "foobarbaz"
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put_situation(scanner)
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# Situation:
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# pos: 0
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# charpos: 0
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# rest: "foobarbaz"
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# rest_size: 9
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```
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The scanner has:
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* A <i>stored string</i>, which is:
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* Initially set by StringScanner.new(string) to the given `string`
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(`'foobarbaz'` in the example above).
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* Modifiable by methods #string=(new_string) and #concat(more_string).
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* Returned by method #string.
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More at [Stored String][1] below.
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* A _position_;
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a zero-based index into the bytes of the stored string (_not_ into its characters):
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* Initially set by StringScanner.new to `0`.
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* Returned by method #pos.
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* Modifiable explicitly by methods #reset, #terminate, and #pos=(new_pos).
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* Modifiable implicitly (various traversing methods, among others).
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More at [Byte Position][2] below.
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* A <i>target substring</i>,
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which is a trailing substring of the stored string;
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it extends from the current position to the end of the stored string:
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* Initially set by StringScanner.new(string) to the given `string`
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(`'foobarbaz'` in the example above).
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* Returned by method #rest.
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* Modified by any modification to either the stored string or the position.
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<b>Most importantly</b>:
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the searching and traversing methods operate on the target substring,
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which may be (and often is) less than the entire stored string.
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More at [Target Substring][3] below.
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## Stored \String
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The <i>stored string</i> is the string stored in the `StringScanner` object.
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Each of these methods sets, modifies, or returns the stored string:
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| Method | Effect |
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|----------------------|-------------------------------------------------|
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| ::new(string) | Creates a new scanner for the given string. |
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| #string=(new_string) | Replaces the existing stored string. |
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| #concat(more_string) | Appends a string to the existing stored string. |
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| #string | Returns the stored string. |
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## Positions
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A `StringScanner` object maintains a zero-based <i>byte position</i>
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and a zero-based <i>character position</i>.
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Each of these methods explicitly sets positions:
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| Method | Effect |
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|--------------------------|----------------------------------------------------------|
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| #reset | Sets both positions to zero (begining of stored string). |
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| #terminate | Sets both positions to the end of the stored string. |
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| #pos=(new_byte_position) | Sets byte position; adjusts character position. |
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### Byte Position (Position)
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The byte position (or simply _position_)
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is a zero-based index into the bytes in the scanner's stored string;
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for a new `StringScanner` object, the byte position is zero.
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When the byte position is:
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* Zero (at the beginning), the target substring is the entire stored string.
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* Equal to the size of the stored string (at the end),
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the target substring is the empty string `''`.
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To get or set the byte position:
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* \#pos: returns the byte position.
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* \#pos=(new_pos): sets the byte position.
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Many methods use the byte position as the basis for finding matches;
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many others set, increment, or decrement the byte position:
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```
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scanner = StringScanner.new('foobar')
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scanner.pos # => 0
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scanner.scan(/foo/) # => "foo" # Match found.
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scanner.pos # => 3 # Byte position incremented.
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scanner.scan(/foo/) # => nil # Match not found.
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scanner.pos # => 3 # Byte position not changed.
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```
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Some methods implicitly modify the byte position;
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see:
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* [Setting the Target Substring][4].
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* [Traversing the Target Substring][5].
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The values of these methods are derived directly from the values of #pos and #string:
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- \#charpos: the [character position][7].
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- \#rest: the [target substring][3].
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- \#rest_size: `rest.size`.
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### Character Position
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The character position is a zero-based index into the _characters_
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in the stored string;
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for a new `StringScanner` object, the character position is zero.
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\Method #charpos returns the character position;
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its value may not be reset explicitly.
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Some methods change (increment or reset) the character position;
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see:
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* [Setting the Target Substring][4].
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* [Traversing the Target Substring][5].
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Example (string includes multi-byte characters):
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```
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scanner = StringScanner.new(ENGLISH_TEXT) # Five 1-byte characters.
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scanner.concat(HIRAGANA_TEXT) # Five 3-byte characters
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scanner.string # => "Helloこんにちは" # Twenty bytes in all.
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put_situation(scanner)
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# Situation:
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# pos: 0
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# charpos: 0
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# rest: "Helloこんにちは"
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# rest_size: 20
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scanner.scan(/Hello/) # => "Hello" # Five 1-byte characters.
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put_situation(scanner)
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# Situation:
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# pos: 5
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# charpos: 5
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# rest: "こんにちは"
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# rest_size: 15
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scanner.getch # => "こ" # One 3-byte character.
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put_situation(scanner)
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# Situation:
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# pos: 8
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# charpos: 6
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# rest: "んにちは"
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# rest_size: 12```
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## Target Substring
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The target substring is the the part of the [stored string][1]
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that extends from the current [byte position][2] to the end of the stored string;
|
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it is always either:
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|
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- The entire stored string (byte position is zero).
|
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- A trailing substring of the stored string (byte position positive).
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|
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The target substring is returned by method #rest,
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and its size is returned by method #rest_size.
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|
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Examples:
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|
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```
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scanner = StringScanner.new('foobarbaz')
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put_situation(scanner)
|
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# Situation:
|
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# pos: 0
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# charpos: 0
|
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# rest: "foobarbaz"
|
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# rest_size: 9
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scanner.pos = 3
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put_situation(scanner)
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# Situation:
|
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# pos: 3
|
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# charpos: 3
|
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# rest: "barbaz"
|
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# rest_size: 6
|
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scanner.pos = 9
|
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put_situation(scanner)
|
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# Situation:
|
||||
# pos: 9
|
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# charpos: 9
|
||||
# rest: ""
|
||||
# rest_size: 0
|
||||
```
|
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|
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### Setting the Target Substring
|
||||
|
||||
The target substring is set whenever:
|
||||
|
||||
* The [stored string][1] is set (position reset to zero; target substring set to stored string).
|
||||
* The [byte position][2] is set (target substring adjusted accordingly).
|
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|
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### Querying the Target Substring
|
||||
|
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This table summarizes (details and examples at the links):
|
||||
|
||||
| Method | Returns |
|
||||
|------------|-----------------------------------|
|
||||
| #rest | Target substring. |
|
||||
| #rest_size | Size (bytes) of target substring. |
|
||||
|
||||
### Searching the Target Substring
|
||||
|
||||
A _search_ method examines the target substring,
|
||||
but does not advance the [positions][11]
|
||||
or (by implication) shorten the target substring.
|
||||
|
||||
This table summarizes (details and examples at the links):
|
||||
|
||||
| Method | Returns | Sets Match Values? |
|
||||
|-----------------------|-----------------------------------------------|--------------------|
|
||||
| #check(pattern) | Matched leading substring or +nil+. | Yes. |
|
||||
| #check_until(pattern) | Matched substring (anywhere) or +nil+. | Yes. |
|
||||
| #exist?(pattern) | Matched substring (anywhere) end index. | Yes. |
|
||||
| #match?(pattern) | Size of matched leading substring or +nil+. | Yes. |
|
||||
| #peek(size) | Leading substring of given length (bytes). | No. |
|
||||
| #peek_byte | Integer leading byte or +nil+. | No. |
|
||||
| #rest | Target substring (from byte position to end). | No. |
|
||||
|
||||
### Traversing the Target Substring
|
||||
|
||||
A _traversal_ method examines the target substring,
|
||||
and, if successful:
|
||||
|
||||
- Advances the [positions][11].
|
||||
- Shortens the target substring.
|
||||
|
||||
|
||||
This table summarizes (details and examples at links):
|
||||
|
||||
| Method | Returns | Sets Match Values? |
|
||||
|----------------------|------------------------------------------------------|--------------------|
|
||||
| #get_byte | Leading byte or +nil+. | No. |
|
||||
| #getch | Leading character or +nil+. | No. |
|
||||
| #scan(pattern) | Matched leading substring or +nil+. | Yes. |
|
||||
| #scan_byte | Integer leading byte or +nil+. | No. |
|
||||
| #scan_until(pattern) | Matched substring (anywhere) or +nil+. | Yes. |
|
||||
| #skip(pattern) | Matched leading substring size or +nil+. | Yes. |
|
||||
| #skip_until(pattern) | Position delta to end-of-matched-substring or +nil+. | Yes. |
|
||||
| #unscan | +self+. | No. |
|
||||
|
||||
## Querying the Scanner
|
||||
|
||||
Each of these methods queries the scanner object
|
||||
without modifying it (details and examples at links)
|
||||
|
||||
| Method | Returns |
|
||||
|---------------------|----------------------------------|
|
||||
| #beginning_of_line? | +true+ or +false+. |
|
||||
| #charpos | Character position. |
|
||||
| #eos? | +true+ or +false+. |
|
||||
| #fixed_anchor? | +true+ or +false+. |
|
||||
| #inspect | String representation of +self+. |
|
||||
| #pos | Byte position. |
|
||||
| #rest | Target substring. |
|
||||
| #rest_size | Size of target substring. |
|
||||
| #string | Stored string. |
|
||||
|
||||
## Matching
|
||||
|
||||
`StringScanner` implements pattern matching via Ruby class [Regexp][6],
|
||||
and its matching behaviors are the same as Ruby's
|
||||
except for the [fixed-anchor property][10].
|
||||
|
||||
### Matcher Methods
|
||||
|
||||
Each <i>matcher method</i> takes a single argument `pattern`,
|
||||
and attempts to find a matching substring in the [target substring][3].
|
||||
|
||||
| Method | Pattern Type | Matches Target Substring | Success Return | May Update Positions? |
|
||||
|--------------|-------------------|--------------------------|--------------------|-----------------------|
|
||||
| #check | Regexp or String. | At beginning. | Matched substring. | No. |
|
||||
| #check_until | Regexp. | Anywhere. | Substring. | No. |
|
||||
| #match? | Regexp or String. | At beginning. | Updated position. | No. |
|
||||
| #exist? | Regexp. | Anywhere. | Updated position. | No. |
|
||||
| #scan | Regexp or String. | At beginning. | Matched substring. | Yes. |
|
||||
| #scan_until | Regexp. | Anywhere. | Substring. | Yes. |
|
||||
| #skip | Regexp or String. | At beginning. | Match size. | Yes. |
|
||||
| #skip_until | Regexp. | Anywhere. | Position delta. | Yes. |
|
||||
|
||||
<br>
|
||||
|
||||
Which matcher you choose will depend on:
|
||||
|
||||
- Where you want to find a match:
|
||||
|
||||
- Only at the beginning of the target substring:
|
||||
#check, #match?, #scan, #skip.
|
||||
- Anywhere in the target substring:
|
||||
#check_until, #exist?, #scan_until, #skip_until.
|
||||
|
||||
- Whether you want to:
|
||||
|
||||
- Traverse, by advancing the positions:
|
||||
#scan, #scan_until, #skip, #skip_until.
|
||||
- Keep the positions unchanged:
|
||||
#check, #check_until, #exist?, #match?.
|
||||
|
||||
- What you want for the return value:
|
||||
|
||||
- The matched substring: #check, #check_until, #scan, #scan_until.
|
||||
- The updated position: #exist?, #match?.
|
||||
- The position delta: #skip_until.
|
||||
- The match size: #skip.
|
||||
|
||||
### Match Values
|
||||
|
||||
The <i>match values</i> in a `StringScanner` object
|
||||
generally contain the results of the most recent attempted match.
|
||||
|
||||
Each match value may be thought of as:
|
||||
|
||||
* _Clear_: Initially, or after an unsuccessful match attempt:
|
||||
usually, `false`, `nil`, or `{}`.
|
||||
* _Set_: After a successful match attempt:
|
||||
`true`, string, array, or hash.
|
||||
|
||||
Each of these methods clears match values:
|
||||
|
||||
- ::new(string).
|
||||
- \#reset.
|
||||
- \#terminate.
|
||||
|
||||
Each of these methods attempts a match based on a pattern,
|
||||
and either sets match values (if successful) or clears them (if not);
|
||||
|
||||
- \#check(pattern)
|
||||
- \#check_until(pattern)
|
||||
- \#exist?(pattern)
|
||||
- \#match?(pattern)
|
||||
- \#scan(pattern)
|
||||
- \#scan_until(pattern)
|
||||
- \#skip(pattern)
|
||||
- \#skip_until(pattern)
|
||||
|
||||
#### Basic Match Values
|
||||
|
||||
Basic match values are those not related to captures.
|
||||
|
||||
Each of these methods returns a basic match value:
|
||||
|
||||
| Method | Return After Match | Return After No Match |
|
||||
|-----------------|----------------------------------------|-----------------------|
|
||||
| #matched? | +true+. | +false+. |
|
||||
| #matched_size | Size of matched substring. | +nil+. |
|
||||
| #matched | Matched substring. | +nil+. |
|
||||
| #pre_match | Substring preceding matched substring. | +nil+. |
|
||||
| #post_match | Substring following matched substring. | +nil+. |
|
||||
|
||||
<br>
|
||||
|
||||
See examples below.
|
||||
|
||||
#### Captured Match Values
|
||||
|
||||
Captured match values are those related to [captures][16].
|
||||
|
||||
Each of these methods returns a captured match value:
|
||||
|
||||
| Method | Return After Match | Return After No Match |
|
||||
|-----------------|-----------------------------------------|-----------------------|
|
||||
| #size | Count of captured substrings. | +nil+. |
|
||||
| #[](n) | <tt>n</tt>th captured substring. | +nil+. |
|
||||
| #captures | Array of all captured substrings. | +nil+. |
|
||||
| #values_at(*n) | Array of specified captured substrings. | +nil+. |
|
||||
| #named_captures | Hash of named captures. | <tt>{}</tt>. |
|
||||
|
||||
<br>
|
||||
|
||||
See examples below.
|
||||
|
||||
#### Match Values Examples
|
||||
|
||||
Successful basic match attempt (no captures):
|
||||
|
||||
```
|
||||
scanner = StringScanner.new('foobarbaz')
|
||||
scanner.exist?(/bar/)
|
||||
put_match_values(scanner)
|
||||
# Basic match values:
|
||||
# matched?: true
|
||||
# matched_size: 3
|
||||
# pre_match: "foo"
|
||||
# matched : "bar"
|
||||
# post_match: "baz"
|
||||
# Captured match values:
|
||||
# size: 1
|
||||
# captures: []
|
||||
# named_captures: {}
|
||||
# values_at: ["bar", nil]
|
||||
# []:
|
||||
# [0]: "bar"
|
||||
# [1]: nil
|
||||
```
|
||||
|
||||
Failed basic match attempt (no captures);
|
||||
|
||||
```
|
||||
scanner = StringScanner.new('foobarbaz')
|
||||
scanner.exist?(/nope/)
|
||||
match_values_cleared?(scanner) # => true
|
||||
```
|
||||
|
||||
Successful unnamed capture match attempt:
|
||||
|
||||
```
|
||||
scanner = StringScanner.new('foobarbazbatbam')
|
||||
scanner.exist?(/(foo)bar(baz)bat(bam)/)
|
||||
put_match_values(scanner)
|
||||
# Basic match values:
|
||||
# matched?: true
|
||||
# matched_size: 15
|
||||
# pre_match: ""
|
||||
# matched : "foobarbazbatbam"
|
||||
# post_match: ""
|
||||
# Captured match values:
|
||||
# size: 4
|
||||
# captures: ["foo", "baz", "bam"]
|
||||
# named_captures: {}
|
||||
# values_at: ["foobarbazbatbam", "foo", "baz", "bam", nil]
|
||||
# []:
|
||||
# [0]: "foobarbazbatbam"
|
||||
# [1]: "foo"
|
||||
# [2]: "baz"
|
||||
# [3]: "bam"
|
||||
# [4]: nil
|
||||
```
|
||||
|
||||
Successful named capture match attempt;
|
||||
same as unnamed above, except for #named_captures:
|
||||
|
||||
```
|
||||
scanner = StringScanner.new('foobarbazbatbam')
|
||||
scanner.exist?(/(?<x>foo)bar(?<y>baz)bat(?<z>bam)/)
|
||||
scanner.named_captures # => {"x"=>"foo", "y"=>"baz", "z"=>"bam"}
|
||||
```
|
||||
|
||||
Failed unnamed capture match attempt:
|
||||
|
||||
```
|
||||
scanner = StringScanner.new('somestring')
|
||||
scanner.exist?(/(foo)bar(baz)bat(bam)/)
|
||||
match_values_cleared?(scanner) # => true
|
||||
```
|
||||
|
||||
Failed named capture match attempt;
|
||||
same as unnamed above, except for #named_captures:
|
||||
|
||||
```
|
||||
scanner = StringScanner.new('somestring')
|
||||
scanner.exist?(/(?<x>foo)bar(?<y>baz)bat(?<z>bam)/)
|
||||
match_values_cleared?(scanner) # => false
|
||||
scanner.named_captures # => {"x"=>nil, "y"=>nil, "z"=>nil}
|
||||
```
|
||||
|
||||
## Fixed-Anchor Property
|
||||
|
||||
Pattern matching in `StringScanner` is the same as in Ruby's,
|
||||
except for its fixed-anchor property,
|
||||
which determines the meaning of `'\A'`:
|
||||
|
||||
* `false` (the default): matches the current byte position.
|
||||
|
||||
```
|
||||
scanner = StringScanner.new('foobar')
|
||||
scanner.scan(/\A./) # => "f"
|
||||
scanner.scan(/\A./) # => "o"
|
||||
scanner.scan(/\A./) # => "o"
|
||||
scanner.scan(/\A./) # => "b"
|
||||
```
|
||||
|
||||
* `true`: matches the beginning of the target substring;
|
||||
never matches unless the byte position is zero:
|
||||
|
||||
```
|
||||
scanner = StringScanner.new('foobar', fixed_anchor: true)
|
||||
scanner.scan(/\A./) # => "f"
|
||||
scanner.scan(/\A./) # => nil
|
||||
scanner.reset
|
||||
scanner.scan(/\A./) # => "f"
|
||||
```
|
||||
|
||||
The fixed-anchor property is set when the `StringScanner` object is created,
|
||||
and may not be modified
|
||||
(see StringScanner.new);
|
||||
method #fixed_anchor? returns the setting.
|
||||
|
||||
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