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