ruby - Fiber.yield using || -

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i following code:

sg = fiber.new     s = 0     loop         square = s * s         s += 1         s = fiber.yield(square) || s     end end  puts sg.resume puts sg.resume puts sg.resume puts sg.resume 40 puts sg.resume puts sg.resume 0 puts sg.resume puts sg.resume

when run, outputs:

0 1 4 1600 1681 0 1 4

how line 6 s = fiber.yield(square) || s work? think understand component parts not line whole doing. (is there alternative way of writing might better me understand?).

(edit: code modified example page 295 'beginning ruby, novice professional 2nd ed' peter cooper.)

according docs yield

any arguments passed next resume value fiber.yield expression evaluates to.

the line

s = fiber.yield(square) || s

assigns argument passed resume s. if value nil (or argument missing), s re-assiged s (i.e. doesn't change).

example:

sg.resume       #=> s = nil || s                 #=> s = s  sg.resume 40    #=> s = 40  || s                 #=> s = 40

another way write is:

result = fiber.yield(square) s = result if result

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