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Returns +self+ with all, a substring, or none of its contents replaced;
returns the argument +other_string+.
<b>Form <tt>self[index] = other_string</tt></b>
With non-negative integer argument +index+ given,
searches for the 1-character substring found in self at character offset index:
s = 'hello'
s[0] = 'foo' # => "foo"
s # => "fooello"
s = 'hello'
s[4] = 'foo' # => "foo"
s # => "hellfoo"
s = 'hello'
s[5] = 'foo' # => "foo"
s # => "hellofoo"
s = 'hello'
s[6] = 'foo' # Raises IndexError: index 6 out of string.
With negative integer argument +index+ given,
counts backward from the end of +self+:
s = 'hello'
s[-1] = 'foo' # => "foo"
s # => "hellfoo"
s = 'hello'
s[-5] = 'foo' # => "foo"
s # => "fooello"
s = 'hello'
s[-6] = 'foo' # Raises IndexError: index -6 out of string.
<b>Form <tt>self[start, length] = other_string</tt></b>
With integer arguments +start+ and +length+ given,
searches for a substring of size +length+ characters (as available)
beginning at character offset specified by +start+.
If argument +start+ is non-negative,
the offset is +start+:
s = 'hello'
s[0, 1] = 'foo' # => "foo"
s # => "fooello"
s = 'hello'
s[0, 5] = 'foo' # => "foo"
s # => "foo"
s = 'hello'
s[0, 9] = 'foo' # => "foo"
s # => "foo"
s = 'hello'
s[2, 0] = 'foo' # => "foo"
s # => "hefoollo"
s = 'hello'
s[2, -1] = 'foo' # Raises IndexError: negative length -1.
If argument +start+ is negative,
counts backward from the end of +self+:
s = 'hello'
s[-1, 1] = 'foo' # => "foo"
s # => "hellfoo"
s = 'hello'
s[-1, 9] = 'foo' # => "foo"
s # => "hellfoo"
s = 'hello'
s[-5, 2] = 'foo' # => "foo"
s # => "foollo"
s = 'hello'
s[-3, 0] = 'foo' # => "foo"
s # => "hefoollo"
s = 'hello'
s[-6, 2] = 'foo' # Raises IndexError: index -6 out of string.
Special case: if +start+ equals the length of +self+,
the argument is appended to +self+:
s = 'hello'
s[5, 3] = 'foo' # => "foo"
s # => "hellofoo"
<b>Form <tt>self[range] = other_string</tt></b>
With Range argument +range+ given,
equivalent to <tt>self[range.start, range.size] = other_string</tt>:
s0 = 'hello'
s1 = 'hello'
s0[0..2] = 'foo' # => "foo"
s1[0, 3] = 'foo' # => "foo"
s0 # => "foolo"
s1 # => "foolo"
s = 'hello'
s[0...2] = 'foo' # => "foo"
s # => "foollo"
s = 'hello'
s[0...0] = 'foo' # => "foo"
s # => "foohello"
s = 'hello'
s[9..10] = 'foo' # Raises RangeError: 9..10 out of range
<b>Form <tt>self[regexp, capture = 0] = other_string</tt></b>
With Regexp argument +regexp+ given and +capture+ as zero,
searches for a matching substring in +self+;
updates {Regexp-related global variables}[rdoc-ref:Regexp@Global+Variables]:
s = 'hello'
s[/l/] = 'L' # => "L"
[$`, $&, $'] # => ["he", "l", "lo"]
s[/eLlo/] = 'owdy' # => "owdy"
[$`, $&, $'] # => ["h", "eLlo", ""]
s[/eLlo/] = 'owdy' # Raises IndexError: regexp not matched.
[$`, $&, $'] # => [nil, nil, nil]
With +capture+ as a positive integer +n+,
searches for the +n+th matched group:
s = 'hello'
s[/(h)(e)(l+)(o)/] = 'foo' # => "foo"
[$`, $&, $'] # => ["", "hello", ""]
s = 'hello'
s[/(h)(e)(l+)(o)/, 1] = 'foo' # => "foo"
s # => "fooello"
[$`, $&, $'] # => ["", "hello", ""]
s = 'hello'
s[/(h)(e)(l+)(o)/, 2] = 'foo' # => "foo"
s # => "hfoollo"
[$`, $&, $'] # => ["", "hello", ""]
s = 'hello'
s[/(h)(e)(l+)(o)/, 4] = 'foo' # => "foo"
s # => "hellfoo"
[$`, $&, $'] # => ["", "hello", ""]
s = 'hello'
# => "hello"
s[/(h)(e)(l+)(o)/, 5] = 'foo # Raises IndexError: index 5 out of regexp.
s = 'hello'
s[/nosuch/] = 'foo' # Raises IndexError: regexp not matched.
<b>Form <tt>self[substring] = other_string</tt></b>
With string argument +substring+ given:
s = 'hello'
s['l'] = 'foo' # => "foo"
s # => "hefoolo"
s = 'hello'
s['ll'] = 'foo' # => "foo"
s # => "hefooo"
s = 'Привет'
s['ив'] = 'foo' # => "foo"
s # => "Прfooет"
s = 'こんにちは'
s['んにち'] = 'foo' # => "foo"
s # => "こfooは"
s['nosuch'] = 'foo' # Raises IndexError: string not matched.
Related: see {Modifying}[rdoc-ref:String@Modifying].
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