如何在Ruby函数调用期间将数组转换为字符串列表

Question

我试图在Ruby中调用RRD.create。我的RRD变量存储在一个散列中，我需要构造一个RRD.create调用。下面是我的代码:

pool_map = {
  "cleanup"  => "Cleaning up",
  "leased" => "Leased",
  "ready"  => "Ready"
}
start = Time.now.to_i
ti = 60 # time interval, in seconds
RRD.create(
         rrdfile,
         "--start", "#{start - 1}",
         "--step",  ti, # seconds
         pool_map.keys.map{|val| "DS:#{val}:GAUGE:#{ti * 2}:0:U" }.collect,
         "RRA:LAST:0.5:1:#{86400 / ti}",         # detailed values for last 24 hours
         "RRA:AVERAGE:0.5:#{5*60 / ti}:#{7*24*60}", # 5 min averages for 7 days
         "RRA:MAX:0.5:#{5*60 / ti}:#{7*24*60}",     # 5 min maximums for 7 days
         "RRA:AVERAGE:0.5:#{60*60 / ti}:#{183*24}", # 1 hour averages for a half of the year
         "RRA:MAX:0.5:#{60*60 / ti}:#{183*24}"      # 1 hour maximums for a half of the year
        )

然而，我从Ruby得到以下错误:

in `create': invalid argument - Array, expected T_STRING or T_FIXNUM on index 5 (TypeError)

我需要指定几个字符串给RRD.create而不是传递数组。我如何在Ruby中做到这一点?

注:http://oss.oetiker.ch/rrdtool/prog/rrdruby.en.html

Answer 1

您需要"splat"操作符(一元星号):

*pool_map.keys.map{|val| ...}

注意，您不需要最后的collect，它什么也不做!collect只是map的别名，你没有对它做任何事情，因为你没有给它传递一个块。

Splat对于解构数组非常有用:

arr = [1, 2, 3]
a, b, c = *arr
# a = 1; b = 2; c = 3

你可以经常用它来给方法提供参数，就像你想做的

def sum_three_numbers(x, y, z)
  x + y + z
end
arr = [1, 2, 3]
sum_three_numbers(*arr)
# => 6
arr = [1, 2]
sum_three_numbers(100, *arr)
# => 103