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/
produces:
Freddie
Herbie
Ron
Max
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"
produces:
0: 0 1 2 3 4
1: 5 6 7 8 9
2: 10 11 12 13 14
3: 15 16
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.
callcc {|cont| cont.call } → nil
callcc {|cont| cont.call 1 } → 1
callcc {|cont| cont.call 1, 2, 3 } → [1, 2, 3]
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.