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Ruby - New Features in Ruby 2.6

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ruby 2.6 多了一些有趣的新特性和功能，來了解一下

Endless ranges

利用 .. 代表無窮的範圍

早期的寫法 100..Float::INFINITY

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n = 123

case n
when 1..9 then 'Single digit'
when 10..99 then 'Two digit'
when 100.. then 'Three or more'
end

# => "Three or more"

但也要小心，會一直跑下去

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(1..).each {|index| puts index }

Kernel#then (Kernel#yield_self alias)

新增一個 yield_self 新的 alias then

主要跟 tap 相反，tap 最後是返回原本的 object，then 則是返回 block

大概是下面這樣的差別

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class Object
  def tap
    yield self
    self
  end

  def then
    yield(self)
  end
end

範例

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3.next.then {|x| x**x }.to_s
#=> "256"
"my string".yield_self {|s| s.upcase }
#=> "MY STRING"

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cisbn = '978-1-93778-549-9'

cisbn.gsub('-', '')
  .then { |isbn| URI("#{API_URL}?q=isbn:#{isbn}") }
  .then { |uri| Net:HTTP.get(uri) }
  .then { |json_response| JSON.parse(json_response) }
  .then { |response| response.dig('items', 'volumeInfo') }

Enumerable#chain and Enumerator#+

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(1..3).chain((5..7), [9, 10]).to_a
# => [1, 2, 3, 5, 6, 7, 9, 10]
(1..3).each + (5..7) + (9..10).to_a
# => [1, 2, 3, 5, 6, 7, 9, 10]

Composition operators << and >> to Proc and Method

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f = proc{|x| x + 2}
g = proc{|x| x * 3}
(f << g).call(3) # -> 11; identical to f(g(3))
(f >> g).call(3) # -> 15; identical to g(f(3))

Array#union and Array#difference

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a = [1, 2, 3]
b = [2, 3, 4]

a.union(b) # => [1, 2, 3, 4]
a.difference(b) # => [1]
a | b # => [1, 2, 3, 4]
a & b # => [2, 3]
a - b # => [1]
a && b # => [2, 3, 4]
a || b # => [1, 2, 3]

Array#filter (Array#select alias)

主要是其他語言 Javascript, PHP, Haskell, Java 8, Scala, R 等等都是用 fliter

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[:foo, :bar].filter { |x| x == :foo }

Enumerable#to_h with block

to_h 支援 block，就可以直接作轉換 key, value

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hash = { foo: 2, bar: 3 }
hash.to_h { |k, v| [k.upcase, v*v] } #=> { FOO: 4, BAR: 9 }

# ruby 2.5:
# hash.map { |k, v| [k.upcase, v*v] }.to_h
# hash.reduce({}) { |result, (k, v)| result.merge(k.upcase => v*v) }

Enumerator::ArithmeticSequence

之前無法用 first 和 last

  • Range#step
  • Numeric#step
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(1..10).step(2).last
# 9

(1..10).step(2).last
# ruby 2.5:
# NoMethodError: undefined method `last' for #<Enumerator: 1..10:step(2)>

% is step alias

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((1..10) % 2).to_a
#  => [1, 3, 5, 7, 9]

另一個改變

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(1..10).step(2) == (1..10).step(2)
# false - Ruby 2.5 (and older)
(1..10).step(2) == (1..10).step(2)
# true - Ruby 2.6

Merge multiple hashes

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a = { a: 1 }
b = { b: 2 }
c = { c: 3 }
a.merge(b, c)
# {:a=>1, :b=>2, :c=>3}


a.merge(b).merge(c)
# ruby 2.5:
# {:a=>1, :b=>2, :c=>3}

Random.bytes

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Random.bytes(8)
# => "\xA4\xFB\xC4\x94\xC5U\xA0\x1A"

# ruby 2.5
Random.new.bytes(10)
# => "\xCEn@\xFA\x93\xB3\xB9\x80p\xA9"

Range#=== now uses uses #cover? instead of #include?

===: case equality，原本是用 include? 的方式，改為用 cover?

  • 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.

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("a".."z").cover?("c")  #=> true
("a".."z").cover?("5")  #=> false
("a".."z").cover?("cc") #=> true
(1..5).cover?(2..3)     #=> true
(1..5).cover?(0..6)     #=> false
(1..5).cover?(1...6)    #=> true

("a".."z").include?("g")   #=> true
("a".."z").include?("A")   #=> false
("a".."z").include?("cc")  #=> false

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require 'date'

case DateTime.now
when Date.today..Date.today+1
  puts 'matched'
else
  puts 'not matched'
end

參考文件

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