ruby - Why does a Flip-Flop operator include the second condition? -
the following code using flip-flop operator.
(1..10).each {|x| print "#{x}," if x==3..x==5 } why results 3,4,5?
i think should 3,4.
as mentioned in tutorial, expression becomes true when x == 3, , continues true until x == 5. how '5' been printed if evaluates false? please clarify me?
the important link, "the ruby programming language" :
when .. , ... operators used in conditional, such if statement, or in loop, such while loop (see chapter 5 more conditionals , loops), not create range objects. instead, create special kind of boolean expression called flip-flop. flip-flop expression evaluates true or false, comparison , equality expressions do. extraordinarily unusual thing flip-flop expression, however, value depends on value of previous evalu- ations. means flip-flop expression has state associated it; must remember information previous evaluations. because has state, expect flip-flop object of sort. isn’t—it’s ruby expression, , ruby interpreter stores state (just single boolean value) requires in internal parsed representation of expression.
with background in mind, consider flip-flop in following code. note first .. in code creates range object. second 1 creates flip-flop expression:
(1..10).each {|x| print x if x==3..x==5 } the flip-flop consists of 2 boolean expressions joined .. operator, in context of conditional or loop. flip-flop expression false unless , until lefthand expression evaluates true. once expression has become true, ex- pression “flips” persistent true state. remains in state, , subsequent evaluations return true until righthand expression evaluates true. when happens, flip-flop “flops” persistent false state. subsequent evaluations of expression return false until lefthand expression becomes true again. in code example, flip-flop evaluated repeatedly, values of x 1 10. starts off in false state, , evaluates false when x 1 , 2. when x==3, flip-flop flips true , returns true. continues return true when x 4 , 5. when x==5, however, flip-flop flops false, , returns false remaining values of x. result code prints 345.
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