Ruby的catch与throw

catch-and-throw-exception-in-ruby

Ruby的 catch 和 throw 不同于其他语言。他的工作方式有点像 Goto。

举个例子：

我们展示下 catch \ throw 正常状态下的执行

# Ruby Program of Catch and Throw Exception
puts '11111'
gfg = catch(:divide) do
  puts '22222'
  # a code block of catch similar to begin
  number = 1
  puts '3333'
  throw :divide if number == 0
  puts '44444'
  number # set gfg = number if
  # no exception is thrown
end
puts '5555'
p gfg
puts ">>>>"

# 输出: 
# 11111
# 22222
# 3333
# 44444
# 5555
# 1
# >>>>

可以看到按照正常输出。

如果我们修改为 number = 0

输出结果将变成

# 11111
# 22222
# 3333
# 5555
# nil
# >>>>

throw 处断开，直接返回到 catch 语句的结果，由于没有值，返回的是 nil

如果我们想赋予默认值可以这样

# Ruby Program of Catch and Throw Exception
puts '11111'
gfg = catch(:divide) do
  puts '22222'
  # a code block of catch similar to begin
  number = 0
  puts '3333'
  throw :divide, 10 if number == 0
  puts '44444'
  number # set gfg = number if
  # no exception is thrown
end
puts '5555'
p gfg
puts ">>>>"

# 输出
# 11111
# 22222
# 3333
# 5555
# 10
# >>>>

throw的第二个参数是默认值。

当然这样看不出 catch、throw 的特殊性。

# Ruby Program of Catch and Throw Exception
gfg = catch(:divide) do
  # a code block of catch similar to begin
    100.times do
      100.times do
        100.times do
          # number = rand(10000)
          number = 0
          # comes out of all of the loops 
          # and goes to catch statement
          throw :divide, 10 if number == 0
        end
      end
    end
    number # set gfg = number if
    # no exception is thrown
end
puts gfg


# 输出
# 10

可以看出，有这个结构，可以轻松的跳出复杂的嵌套。