ruby

那些奇怪的语法

数组切片

a = [1,2,3,4] => [1, 2, 3, 4] a[4] => nil a[0,1] => [1] a[0..1] => [1, 2] a[0...1] => [1] a[0,0] => [] a[3,0] => [] a[3,4] => [4] a[2,10] => [3, 4] a[4] # 这一行+下几行会非常奇怪 => nil a[4,10] => [] # a[4]明明已经nil了，居然还是[] a[5] => nil # a[5]是nil,可和a[4]不同得到的是nil a[5,10] => nil

hash(dict)默认值

d = Hash.new([]) => {} d[:one] << 'a' => ["a"] d[:two] << 'b' => ["a", "b"] d[:one] => ["a", "b"] d[:three] => ["a", "b"]

需要这样避免

hash = Hash.new {|hash, key| hash[key] = [] }
hash[:one] << "uno"
hash[:two] << "dos"

assert_equal ['uno'], hash[:one]
assert_equal ['dos'], hash[:two]
assert_equal [], hash[:three]