經常會使用 range 去判斷某個值，是否在某個區間
ruby 也提供很多好用的方法去判斷，cover?, include? 等等
Range
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| #... 不包含結尾
(-1..-5).to_a #=> []
(-5..-1).to_a #=> [-5, -4, -3, -2, -1]
('a'..'e').to_a #=> ["a", "b", "c", "d", "e"]
('a'...'e').to_a #=> ["a", "b", "c", "d"]
(0..2) == Range.new(0,2) #=> true
(0..2) == (0...2) #=> false
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begin/end first/last
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| r1 = 3..6
r2 = 3...6
r1a, r1b = r1.first, r1.last #=> 3, 6
r1c, r1d = r1.begin, r1.end #=> 3, 6
r2a, r2b = r2.begin, r2.end #=> 3, 6 (注意：不是3和5)
r1.first(2) #=> [3, 4]
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step
從 0..20 中取出 0，5，10，20
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| a = 0..20
a.step(5).to_a
#=> [0, 5, 10, 15, 20]
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include?/cover?
判斷值，是否在 range 當中
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| r = 1 .. 5
r.include?(1) #=> true
r.include?(0) #=> false
r.cover?(1) #=> true
r.cover?(0) #=> false
("a".."z").include?("ab") # => false
("a".."z").cover?("ab") # => true
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主要差異是
- include? 會將所有值一一拿出來做比對，因此效率較差
- cover? 只會取出開頭和結尾，去比對，值 >= 開頭 && 值 <= 結尾，效能比較好
cover?
Returns true if obj is between the begin and end of the range.
This tests begin <= obj <= end when exclude_end? is false and begin <= obj < end when exclude_end? is true.
官方文件：
參考文件：