1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
|
== \String Slices
A _slice_ of a string is a substring that is selected by certain criteria.
These instance methods make use of slicing:
- String#[] (also aliased as String#slice) returns a slice copied from +self+.
- String#[]= returns a copy of +self+ with a slice replaced.
- String#slice! returns +self+ with a slice removed.
Each of the above methods takes arguments that determine the slice
to be copied or replaced.
The arguments have several forms.
For string +string+, the forms are:
- <tt>string[index]</tt>.
- <tt>string[start, length]</tt>.
- <tt>string[range]</tt>.
- <tt>string[regexp, capture = 0]</tt>.
- <tt>string[substring]</tt>.
<b><tt>string[index]</tt></b>
When non-negative integer argument +index+ is given,
the slice is the 1-character substring found in +self+ at character offset +index+:
'bar'[0] # => "b"
'bar'[2] # => "r"
'bar'[20] # => nil
'тест'[2] # => "с"
'こんにちは'[4] # => "は"
When negative integer +index+ is given,
the slice begins at the offset given by counting backward from the end of +self+:
'bar'[-3] # => "b"
'bar'[-1] # => "r"
'bar'[-20] # => nil
<b><tt>string[start, length]</tt></b>
When non-negative integer arguments +start+ and +length+ are given,
the slice begins at character offset +start+, if it exists,
and continues for +length+ characters, if available:
'foo'[0, 2] # => "fo"
'тест'[1, 2] # => "ес"
'こんにちは'[2, 2] # => "にち"
# Zero length.
'foo'[2, 0] # => ""
# Length not entirely available.
'foo'[1, 200] # => "oo"
# Start out of range.
'foo'[4, 2] # => nil
Special case: if +start+ is equal to the length of +self+,
the slice is a new empty string:
'foo'[3, 2] # => ""
'foo'[3, 200] # => ""
When negative +start+ and non-negative +length+ are given,
the slice beginning is determined by counting backward from the end of +self+,
and the slice continues for +length+ characters, if available:
'foo'[-2, 2] # => "oo"
'foo'[-2, 200] # => "oo"
# Start out of range.
'foo'[-4, 2] # => nil
When negative +length+ is given, there is no slice:
'foo'[1, -1] # => nil
'foo'[-2, -1] # => nil
<b><tt>string[range]</tt></b>
When Range argument +range+ is given,
creates a substring of +string+ using the indices in +range+.
The slice is then determined as above:
'foo'[0..1] # => "fo"
'foo'[0, 2] # => "fo"
'foo'[2...2] # => ""
'foo'[2, 0] # => ""
'foo'[1..200] # => "oo"
'foo'[1, 200] # => "oo"
'foo'[4..5] # => nil
'foo'[4, 2] # => nil
'foo'[-4..-3] # => nil
'foo'[-4, 2] # => nil
'foo'[3..4] # => ""
'foo'[3, 2] # => ""
'foo'[-2..-1] # => "oo"
'foo'[-2, 2] # => "oo"
'foo'[-2..197] # => "oo"
'foo'[-2, 200] # => "oo"
<b><tt>string[regexp, capture = 0]</tt></b>
When the \Regexp argument +regexp+ is given,
and the +capture+ argument is <tt>0</tt>,
the slice is the first matching substring found in +self+:
'foo'[/o/] # => "o"
'foo'[/x/] # => nil
s = 'hello there'
s[/[aeiou](.)\1/] # => "ell"
s[/[aeiou](.)\1/, 0] # => "ell"
If argument +capture+ is given and not <tt>0</tt>,
it should be either an capture group index (integer)
or a capture group name (string or symbol);
the slice is the specified capture (see Regexp@Capturing):
s = 'hello there'
s[/[aeiou](.)\1/, 1] # => "l"
s[/(?<vowel>[aeiou])(?<non_vowel>[^aeiou])/, "non_vowel"] # => "l"
s[/(?<vowel>[aeiou])(?<non_vowel>[^aeiou])/, :vowel] # => "e"
If an invalid capture group index is given, there is no slice.
If an invalid capture group name is given, +IndexError+ is raised.
<b><tt>string[substring]</tt></b>
When the single \String argument +substring+ is given,
returns the substring from +self+ if found, otherwise +nil+:
'foo'['oo'] # => "oo"
'foo'['xx'] # => nil
|
