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[DOC] Refine flip-flop

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Nobuyoshi Nakada 2022-03-24 19:08:18 +09:00
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doc/syntax/control_expressions.rdoc
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@ -513,9 +513,9 @@ and modifier +if+ has lower precedence than <code>=</code>.
== Flip-Flop == Flip-Flop
The flip-flop is a rarely seen conditional expression. It's primary use is The flip-flop is a slightly special conditional expression. One of its
for processing text from ruby one-line programs used with <code>ruby -n</code> typical uses is processing text from ruby one-line programs used with
or <code>ruby -p</code>. <code>ruby -n</code> or <code>ruby -p</code>.
The form of the flip-flop is an expression that indicates when the The form of the flip-flop is an expression that indicates when the
flip-flop turns on, <code>..</code> (or <code>...</code>), then an expression flip-flop turns on, <code>..</code> (or <code>...</code>), then an expression
@ -524,7 +524,6 @@ will continue to evaluate to +true+, and +false+ when off.
Here is an example: Here is an example:
selected = [] selected = []
0.upto 10 do |value| 0.upto 10 do |value|
@ -533,15 +532,16 @@ Here is an example:
p selected # prints [2, 3, 4, 5, 6, 7, 8] p selected # prints [2, 3, 4, 5, 6, 7, 8]
In the above example, the on condition is <code>n==2</code>. The flip-flop In the above example, the `on' condition is <code>n==2</code>. The flip-flop
is initially off (false) for 0 and 1, but becomes on (true) for 2 and remains is initially `off' (false) for 0 and 1, but becomes `on' (true) for 2 and
on through 8. After 8 it turns off and remains off for 9 and 10. remains `on' through 8. After 8 it turns off and remains `off' for 9 and 10.
The flip-flop must be used inside a conditional such as +if+, +while+, The flip-flop must be used inside a conditional such as <code>!</code>,
+unless+, +until+ etc. including the modifier forms. <code>? :</code>, +not+, +if+, +while+, +unless+, +until+ etc. including the
modifier forms.
When you use an inclusive range (<code>..</code>), the off condition is When you use an inclusive range (<code>..</code>), the `off' condition is
evaluated when the on condition changes: evaluated when the `on' condition changes:
selected = [] selected = []
@ -555,7 +555,7 @@ Here, both sides of the flip-flop are evaluated so the flip-flop turns on and
off only when +value+ equals 2. Since the flip-flop turned on in the off only when +value+ equals 2. Since the flip-flop turned on in the
iteration it returns true. iteration it returns true.
When you use an exclusive range (<code>...</code>), the off condition is When you use an exclusive range (<code>...</code>), the `off' condition is
evaluated on the following iteration: evaluated on the following iteration:
selected = [] selected = []
@ -567,5 +567,5 @@ evaluated on the following iteration:
p selected # prints [2, 3, 4, 5] p selected # prints [2, 3, 4, 5]
Here, the flip-flop turns on when +value+ equals 2, but doesn't turn off on the Here, the flip-flop turns on when +value+ equals 2, but doesn't turn off on the
same iteration. The off condition isn't evaluated until the following same iteration. The `off' condition isn't evaluated until the following
iteration and +value+ will never be two again. iteration and +value+ will never be two again.