Question

As every Ruby programmer eventually discovers, calling blocks or procs that contain return statements can be dangerous as this might exit your current context:

def some_method(&_block)
   puts 1
   yield
   # The following line will never be executed in this example
   # as the yield is actually a `yield-and-return`.
   puts 3
end

def test
  some_method do
    puts 2
    return
  end
end

test

# This prints "1\n2\n" instead of "1\n2\n3\n"

In cases you want to be absolutely sure some of your code runs after you called a block or proc, you can use a begin ... ensure construct. But since ensure is also called if there is an exception during yield, it requires a little more work.

I've created a tiny module中检索以两种不同方式处理此问题的“href”值：

使用safe_yield，检测生成的块或proc是否实际使用return关键字返回。如果是这样，它会引发异常。

unknown_block = proc do
  return
end 

ReturnSafeYield.safe_yield(unknown_block)
# => Raises a UnexpectedReturnException exception

使用call_then_yield，您可以调用一个块，然后确保执行第二个块，即使第一个块包含return语句。

unknown_block = proc do
  return
end
ReturnSafeYield.call_then_yield(unknown_block) do
  # => This line is called even though the above block contains a `return`.
end

我正在考虑用这个创建一个快速的Gem，还是有任何内置的解决方案来阻止我错过的嵌套块的快速返回？

Answer 1

有一个内置的解决方案来检测一个块是否包含return语句。

您可以使用RubyVM::InstructionSequence.disasm反汇编用户传入的数据块，然后搜索throw 1，代表return语句。

以下是一个示例实现：

def safe_yield(&block)
  if RubyVM::InstructionSequence.disasm(block) =~ /^\d+ throw +1$/
    raise LocalJumpError
  end

  block.call
end

以下是您如何将其合并到图书馆中的信息：

def library_method(&block)
  safe_yield(&block)
  puts "library_method succeeded"
rescue LocalJumpError
  puts "library_method encountered illegal return but resumed execution"
end

这是一个行为良好且行为不端的用户的用户体验：

def nice_user_method
  library_method { 1 + 1 }
end

nice_user_method
# library_method succeeded

def naughty_user_method
  library_method { return false if rand > 0.5 }
end

naughty_user_method
# library_method encountered illegal return but resumed execution

<强>评论：

使用raise LocalJumpError / rescue LocalJumpError可以解决使用毯子ensure时遇到的问题。

我之所以选择LocalJumpError是因为它看起来很相关，而且因为（我认为！）没有可能导致LocalJumpError被提升的Ruby代码＃34;自然而然地＃34;在这种背景下。如果结果是假的，您可以轻松替换自己的新异常类。

How to prevent problems with `return` from block when using Ruby `yield`

1 个答案: