Question

是否可以构建一个block / rescue链，就像这个动态一样，例如来自符号数组[:f1, :f2, :f3, f4]。下面的代码应该模仿我写的静态：

  begin
    applyF1()
  rescue
    applyF2()
    begin
      applyF3()
    rescue
      applyF4()
    end
  end

我已经知道如何从符号（object.send(message)）发送内置消息，因此applyFx不是问题。

Answer 1

不确定你真正期望的行为，因为@sawa，我不认为你同样对待applyF{1..4}。

此代码段显示了如何依次评估一些lambda，直到其中一个lambdas返回非假值而不提高任何值。

如果您要成对评估applyF{1..?}（F1失败时，请按F2进行恢复，然后尝试使用F3并在失败时按F4进行恢复，等等），你可以让applyF{2,4,..}总是返回nil。

#!/usr/bin/env ruby

blocks = {
  a: ->(){ raise "raise" },
  b: ->(){ raise "also raise" },
  c: ->(){ :finished },
  d: ->(){ "won't be executed" },
}

ret = blocks.reduce(nil) do |has_succeeded, (key, lam)|
  has_succeeded ||=
  begin
    puts "trying #{key.inspect}"
    lam.call # when succeed, the lambda should return a non-false value
  rescue => e
    puts "failed with message=<#{e.message}>. trying next"
    nil
    # no else clause here, so
    # if lam.call raises nothing, memo keep its return value, and prevents calling following {lam}s.
    # if something is raised in lam.call, this block evalutes to nil
  end
end

# will print:
# trying :a
# failed with message=<raise>. trying next
# trying :b
# failed with message=<also raise>. trying next
# trying :c

p ret
# => :finished

参考：How is the value of a begin block determined?

Answer 2

这是我想到的第一个：

def rescueChain(*args)
  args.each do |f|
    begin
      <... apply f here ...>
      return  # Exits from the entire function.
    rescue
    end
  end
end

我还没有测试过。

如何动态建立拦截救援链？

2 个答案: