98 lines
3.4 KiB
Plaintext
98 lines
3.4 KiB
Plaintext
== Character Selectors
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=== Character Selector
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A _character_ _selector_ is a string argument accepted by certain Ruby methods.
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Each of these instance methods accepts one or more character selectors:
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- String#tr(selector, replacements): returns a new string.
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- String#tr!(selector, replacements): returns +self+ or +nil+.
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- String#tr_s(selector, replacements): returns a new string.
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- String#tr_s!(selector, replacements): returns +self+ or +nil+.
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- String#count(*selectors): returns the count of the specified characters.
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- String#delete(*selectors): returns a new string.
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- String#delete!(*selectors): returns +self+ or +nil+.
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- String#squeeze(*selectors): returns a new string.
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- String#squeeze!(*selectors): returns +self+ or +nil+.
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A character selector identifies zero or more characters in +self+
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that are to be operands for the method.
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In this section, we illustrate using method String#delete(selector),
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which deletes the selected characters.
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In the simplest case, the characters selected are exactly those
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contained in the selector itself:
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'abracadabra'.delete('a') # => "brcdbr"
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'abracadabra'.delete('ab') # => "rcdr"
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'abracadabra'.delete('abc') # => "rdr"
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'0123456789'.delete('258') # => "0134679"
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'!@#$%&*()_+'.delete('+&#') # => "!@$%*()_"
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'тест'.delete('т') # => "ес"
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'こんにちは'.delete('に') # => "こんちは"
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Note that order and repetitions do not matter:
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'abracadabra'.delete('dcab') # => "rr"
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'abracadabra'.delete('aaaa') # => "brcdbr"
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In a character selector, these three characters get special treatment:
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- A leading caret (<tt>'^'</tt>) functions as a "not" operator
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for the characters to its right:
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'abracadabra'.delete('^bc') # => "bcb"
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'0123456789'.delete('^852') # => "258"
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- A hyphen (<tt>'-'</tt>) between two other characters
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defines a range of characters instead of a plain string of characters:
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'abracadabra'.delete('a-d') # => "rr"
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'0123456789'.delete('4-7') # => "012389"
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'!@#$%&*()_+'.delete(' -/') # => "@^_"
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# May contain more than one range.
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'abracadabra'.delete('a-cq-t') # => "d"
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# Ranges may be mixed with plain characters.
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'0123456789'.delete('67-950-23') # => "4"
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# Ranges may be mixed with negations.
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'abracadabra'.delete('^a-c') # => "abacaaba"
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- A backslash (<tt>'\'</tt>) acts as an escape for a caret, a hyphen,
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or another backslash:
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'abracadabra^'.delete('\^bc') # => "araadara"
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'abracadabra-'.delete('a\-d') # => "brcbr"
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"hello\r\nworld".delete("\r") # => "hello\nworld"
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"hello\r\nworld".delete("\\r") # => "hello\r\nwold"
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"hello\r\nworld".delete("\\\r") # => "hello\nworld"
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=== Multiple Character Selectors
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These instance methods accept multiple character selectors:
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- String#count(*selectors): returns the count of the specified characters.
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- String#delete(*selectors): returns a new string.
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- String#delete!(*selectors): returns +self+ or +nil+.
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- String#squeeze(*selectors): returns a new string.
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- String#squeeze!(*selectors): returns +self+ or +nil+.
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In effect, the given selectors are formed into a single selector
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consisting of only those characters common to _all_ of the given selectors.
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All forms of selectors may be used, including negations, ranges, and escapes.
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Each of these pairs of method calls is equivalent:
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s.delete('abcde', 'dcbfg')
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s.delete('bcd')
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s.delete('^abc', '^def')
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s.delete('^abcdef')
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s.delete('a-e', 'c-g')
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s.delete('cde')
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