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For an ordinary string, this method, +String#dump+,
returns a printable ASCII-only version of +self+, enclosed in double-quotes.
For a dumped string, method String#undump is the inverse of +String#dump+;
it returns a "restored" version of +self+,
where all the dumping changes have been undone.
In the simplest case, the dumped string contains the original string,
enclosed in double-quotes;
this example is done in +irb+ (interactive Ruby), which uses method `inspect` to render the results:
s = 'hello' # => "hello"
s.dump # => "\"hello\""
s.dump.undump # => "hello"
Keep in mind that in the second line above:
- The outer double-quotes are put on by +inspect+,
and _are_ _not_ part of the output of #dump.
- The inner double-quotes _are_ part of the output of +dump+,
and are escaped by +inspect+ because they are within the outer double-quotes.
To avoid confusion, we'll use this helper method to omit the outer double-quotes:
def dump(s)
print "String: ", s, "\n"
print "Dumped: ", s.dump, "\n"
print "Undumped: ", s.dump.undump, "\n"
end
So that for string <tt>'hello'</tt>, we'll see:
String: hello
Dumped: "hello"
Undumped: hello
In a dump, certain special characters are escaped:
String: "
Dumped: "\""
Undumped: "
String: \
Dumped: "\\"
Undumped: \
In a dump, unprintable characters are replaced by printable ones;
the unprintable characters are the whitespace characters (other than space itself);
here we see the ordinals for those characers, together with explanatory text:
h = {
7 => 'Alert (BEL)',
8 => 'Backspace (BS)',
9 => 'Horizontal tab (HT)',
10 => 'Linefeed (LF)',
11 => 'Vertical tab (VT)',
12 => 'Formfeed (FF)',
13 => 'Carriage return (CR)'
}
In this example, the dumped output is printed by method #inspect,
and so contains both outer double-quotes and escaped inner double-quotes:
s = ''
h.keys.each {|i| s << i } # => [7, 8, 9, 10, 11, 12, 13]
s # => "\a\b\t\n\v\f\r"
s.dump # => "\"\\a\\b\\t\\n\\v\\f\\r\""
If +self+ is encoded in UTF-8 and contains Unicode characters,
each Unicode character is dumped as a Unicode escape sequence:
String: こんにちは
Dumped: "\u3053\u3093\u306B\u3061\u306F"
Undumped: こんにちは
If the encoding of +self+ is not ASCII-compatible
(i.e., if <tt>self.encoding.ascii_compatible?</tt> returns +false+),
each ASCII-compatible byte is dumped as an ASCII character,
and all other bytes are dumped as hexadecimal;
also appends <tt>.dup.force_encoding(\"encoding\")</tt>,
where <tt><encoding></tt> is <tt>self.encoding.name</tt>:
String: hello
Dumped: "\xFE\xFF\x00h\x00e\x00l\x00l\x00o".dup.force_encoding("UTF-16")
Undumped: hello
String: こんにちは
Dumped: "\xFE\xFF0S0\x930k0a0o".dup.force_encoding("UTF-16")
Undumped: こんにちは
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