這幾天在看 Programming Ruby (2nd. Ed.)
看到 Array 部分時，好奇試了這些個東西
a = ["a", "b", "c", "d", "e"] a[3, -2] a[3..1] a[-1..1] a[-1..-3]
結果
a[3, -2] => nil a[3..1] => [] a[-1..1] => [] a[-1..-3] => []
我想要是我來設計，大概會給它弄成這樣
a[3, -2] => ["d", "c"] a[3..1] => ["d", "c", "b"] a[-1..1] => ["e", "d", "c", "b"] a[-1..-3] => ["e", "d", "c"]
因為既然負的 index 是由最後往前數（a[-1] => “e”），我會覺得取好幾個也要有由後往前取的功能 😛
- 留言者: T55555
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- 日期: 2005-09-01 19:21:15
Welcome to the Ruby World.
The [] rule is also apply to []=
So, if a = [‘a’, ‘b’, ‘c’, ‘d’, ‘e’]
and if a[3..1] => [‘d’, ‘c’, ‘b’]
What you would like to see if you write something like
a[3..1] = [1, 2, 3, 4] ?
a will become to [‘a’, 4, 3, 2, 1, ‘e’] ?
One good thing about Ruby is everything are open.
Even the core library.
There are also calibre and facets project to change the array index to the way they like.
I can easily change the length negative value behavior as you like ( the Range one, leave to yourself to do it) , for example :
class Array
alias_method :old, :"[]"
def [](*args) # define my new [] method for Array
begin
old(*args) unless args.length == 2 && args.last < 0
(0...-args.last).inject([]) { |a, i| a << self.slice(args.first - i) }
rescue
old(*args)
end
end
end
a = %w[a b c d e] #=> a = ['a', 'b', 'c', 'd', 'e']
a[3, -2] #=> ['d', 'c']
So, if you don’t like the default way, change to what you like.
On Ruby, you could even change 1+1 to become 3 if you like. 🙂
- 留言者: JiaYun
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- 日期: 2005-09-01 20:41:12
Yes, I will let a be [‘a’, 4, 3, 2, 1, ‘e’] after a[3..1] = [1, 2, 3, 4].
And I finished the homework, but only [] not []=.
class Array
alias_method :old, :"[]"
def [](*args) # define my new [] method for Array
begin
if (args.length == 2 && args.last < 0)
(0...-args.last).inject([]) { |a, i| a << self.slice(args.first - i) }
elsif (args.length == 1 && args.first.class == Range)
range = args.first
first = range.first < 0 ? range.first + self.length : range.first
last = range.last < 0 ? range.last + self.length : range.last
if (first > last)
length = (first - last).abs
length += 1 unless range.exclude_end?
(0...length).inject([]) { |a, i| a << self.slice(range.first - i) }
else
old(*args)
end
else
old(*args)
end
rescue
old(*args)
end
end
end
a = %w[a b c d e]
a[-1..-3] #=> ["e", "d", "c"]
a[-1...-3] #=> ["e", "d"]
a[-1..1] #=> ["e", "d", "c", "b"]
a[-1...1] #=> ["e", "d", "c"]
a[4..2] #=> ["e", "d", "c"]
a[4...2] #=> ["e", "d"]
- 留言者: T55555
- Email: ruby55555@gmail.com
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- 日期: 2005-09-02 00:09:54
Ooops, I found my bug …
The line
old(*args) unless args.length == 2 && args.last < 0
should be like
return old(*args) unless args.length == 2 && args.last < 0