循环控制与休息下一步和重做

可以使用 break，next 和 redo 语句来控制 Ruby 块的执行流程。

break

break 语句将立即退出块。将跳过块中的任何剩余指令，迭代将结束：

actions = %w(run jump swim exit macarena)
index = 0

while index < actions.length
  action = actions[index]

  break if action == "exit"

  index += 1
  puts "Currently doing this action: #{action}"
end

# Currently doing this action: run
# Currently doing this action: jump
# Currently doing this action: swim

next

next 语句将立即返回到块的顶部，并继续下一次迭代。将跳过块中的任何剩余指令：

actions = %w(run jump swim rest macarena)
index = 0

while index < actions.length
  action = actions[index]
  index += 1

  next if action == "rest"

  puts "Currently doing this action: #{action}"
end

# Currently doing this action: run
# Currently doing this action: jump
# Currently doing this action: swim
# Currently doing this action: macarena

redo

redo 语句将立即返回到块的顶部，并重试相同的迭代。将跳过块中的任何剩余指令：

actions = %w(run jump swim sleep macarena)
index = 0
repeat_count = 0

while index < actions.length
  action = actions[index]
  puts "Currently doing this action: #{action}"

  if action == "sleep"
    repeat_count += 1
    redo if repeat_count < 3
  end

  index += 1
end

# Currently doing this action: run
# Currently doing this action: jump
# Currently doing this action: swim
# Currently doing this action: sleep
# Currently doing this action: sleep
# Currently doing this action: sleep
# Currently doing this action: macarena

Enumerable 迭代

除了循环之外，这些语句还使用了 Enumerable 迭代方法，例如 each 和 map：

[1, 2, 3].each do |item|
  next if item.even?
  puts "Item: #{item}"
end

# Item: 1
# Item: 3

阻止结果值

在 break 和 next 语句中，可以提供一个值，并将其用作块结果值：

even_value = for value in [1, 2, 3]
  break value if value.even?
end

puts "The first even value is: #{even_value}"

# The first even value is: 2