Class

Continuation

Inheritance
< Object

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

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"

produces:

   0:   0  1  2  3  4
   1:   5  6  7  8  9
   2:  10 11 12 13 14
   3:  15 16

Methods

Instance

Visibility Signature
public [] (...)
public call (...)

Instance Method Detail

cont.call(args, ...)
cont[args, ...]

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.

   callcc {|cont|  cont.call }           #=> nil
   callcc {|cont|  cont.call 1 }         #=> 1
   callcc {|cont|  cont.call 1, 2, 3 }   #=> [1, 2, 3]

cont.call(args, ...)
cont[args, ...]

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.

   callcc {|cont|  cont.call }           #=> nil
   callcc {|cont|  cont.call 1 }         #=> 1
   callcc {|cont|  cont.call 1, 2, 3 }   #=> [1, 2, 3]