分享两篇文章，介绍Splat operator和Ruby2.0引入的Double Splat operator.
Splat goes Ruby
Drat! - Ruby has a Double Splat
Splat的用法：
- 使用在方法参数中，转化list为Array
def ahoy(*args)
p args
end
ahoy :a, 345, hello: :world # => [:a, 345, {:hello=>:world}]
- 将Array参数转化为list
def ahoy(from, to)
puts "#{to.capitalize}, #{from.capitalize} says ahoy!"
end
even_stephens = %w(steven stephen)
ahoy even_stephens # Array is interpreted as the first argument, and to_matey won’t be set. An ArgumentError is raised.
ahoy *even_stephens # Array is reversed to a list and all the arguments are filled out.
# => Stephen, Steven says ahoy!
- splat后面不能有required参数
def hello(name, *args, options, &block)
p name
p args
p options
p block
end
hello('denny', :a, :b, upcase: true) { 'block this!' }
# name: ”denny”
# args: [:a, :b]
# options: {:upcase=>true}
# => #
# Works fine:
def hello(name = nil, *args)
# Throws SyntaxError:
def hello(*args, name = nil)
# Using several splats in a definition SyntaxErrors too:
def hello(a, *args, b, *brgs)
- 可以在yield参数里
ActiveSupport::Notifications.subscribe('render') do |name, start, finish, id, payload|
puts payload
end
ActiveSupport::Notifications.subscribe('render') do |*, payload|
puts payload
end
# It's also easier than:
ActiveSupport::Notifications.subscribe('render') do |*args|
payload = args.last
puts payload
end
- 赋值时的使用
a, b = [:a, :b]
a # => :a
b # => :b
a, b = [:a, :b, :c] # :c is lost
a # => :a
b # => :b
a, *rest = [:a, :b, :c]
a # => :a
rest # => [:b, :c]
a, *= [:a, :b, :c]
a # => :a
a ,= [:a, :b, :c]
a # => :a
- 如果不关心这个参数就不需要为这个参数命名
class WhipperSnapper
def initialize(snap_count, whip_size)
@snap_count, @whip_size = snap_count, whip_size
end
end
class SupremeSnapper < WhipperSnapper
def initialize(*)
super
@agility = 100_000
end
end
Double Splat的用法
- Obligatorily Optional(如何翻译？)
def hello(**options)
p options
end
hello
# options: {}
hello name: 'Kasper'
# options: { :name => 'Kasper' }
类似于optional arguments
def hello(options = {})
end
- Hash
def hello(name = nil, **options)
p name
p options
end
hello 'Kasper'
# name: 'Kasper'
# options: {}
hello upcase: true
# name: nil
# options: { :upcase => true }
**之前的参数必须是可选的！
def hello(name, **options)
p name
p options
end
hello upcase: true
# name: { :upcase => true }
# options: {}
- Off Key Splat
使用了double splats 之后可以传入或多或少的keys
def hello(name:)
p name
end
hello # raises "ArgumentError: missing keyword: name" as expected
hello name: 'Kasper', play_style: :laces_out
# raises "ArgumentError: unknown keyword: play_style"
def hello(name:, **options)
p name
p options
end
hello name: 'Kasper', play_style: :laces_out
# name: 'Kasper'
# options: { :play_style => :laces_out }
hello play_style: :laces_out
# ArgumentError: missing keyword: name
# 加入默认值后
def hello(name: nil, **options)
p name
p options
end
hello play_style: :laces_out
# nil
# {:play_style=>:laces_out}
- Exploit a Splat, Expand a Hash
可以展开一个hash
options = { a: 'b' }
{ c: 'd', **options } # => { :c => "d", :a => "b" }
*可以展开一个数组，两个用法还是挺接近的。
a=[1,3]
# => [1, 3]
[2, *a]
# => [2, 1, 3]
- Yield to Splat
之前可以这么写
def hello
yield name: 'Kasper'
end
hello { |options| p options[:name] }
# Outputs "Kasper"
可以简写
hello { |name:| p name }
# Outputs "Kasper"
def hello
yield name: 'Kasper', play_style: :laces_out
end
hello { |name:, **| p name }
# Outputs "Kasper"