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Programming Ruby The Pragmatic Programmer's Guide |
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class Continuation
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Parent:
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Object
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Version:
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1.6
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Index:
call
Continuation objects are generated by
Kernel#callcc
. They hold a return address and execution
context, allowing a nonlocal return to the end of the callcc
block from anywhere within a program. Continuations are somewhat
analogous to a structured version of C's setjmp/longjmp
(although they contain more state, so you might consider them closer
to threads).
For instance:
arr = [ "Freddie", "Herbie", "Ron", "Max", "Ringo" ]
callcc{|$cc|}
puts(message = arr.shift)
$cc.call unless message =~ /Max/
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produces:
This (somewhat contrived) example allows the inner loop to abandon
processing early:
callcc {|cont|
for i in 0..4
print "\n#{i}: "
for j in i*5...(i+1)*5
cont.call() if j == 17
printf "%3d", j
end
end
}
print "\n"
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produces:
0: 0 1 2 3 4
1: 5 6 7 8 9
2: 10 11 12 13 14
3: 15 16
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instance methods
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call
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cont.call( [ args ]* )
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Invokes the continuation. The program continues from the end of
the callcc block. If no arguments are given, the original callcc returns nil. If one argument is given, callcc returns it. Otherwise, an array containing args is returned.
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callcc {|cont| cont.call }
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nil
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callcc {|cont| cont.call 1 }
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1
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callcc {|cont| cont.call 1, 2, 3 }
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[1, 2, 3]
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Extracted from the book "Programming Ruby -
The Pragmatic Programmer's Guide"
Copyright
©
2001 by Addison Wesley Longman, Inc. This material may
be distributed only subject to the terms and conditions set forth in
the Open Publication License, v1.0 or later (the latest version is
presently available at http://www.opencontent.org/openpub/)).
Distribution of substantively modified versions of this document is
prohibited without the explicit permission of the copyright holder.
Distribution of the work or derivative of the work in any standard
(paper) book form is prohibited unless prior permission is obtained
from the copyright holder.
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