“返回”行为ruby 块中的关键字

发布于 2024-11-02 16:19:45 字数 428 浏览 4 评论 0原文

有人可以解释以下行为：

def iterate
  return yield
  return "end of iterate"
end

def test_iterate
  assert_equal( "end of iterate",  iterate { return "end of block" } )
  assert_equal( "end of block",  iterate { "end of block" } )
end

我理解 Procs （这就是块）应该在它们被调用的范围内返回。（与 lambda 不同）考虑到这一点，测试中的两个调用不应该返回“块结束”吗？

此测试通过“ruby 1.8.7 (2009-06-12 patchlevel 174) [universal-darwin10.0]”( OSX 10.6.7 )

原文

Can someone explain the behavior of the following

def iterate
  return yield
  return "end of iterate"
end

def test_iterate
  assert_equal( "end of iterate",  iterate { return "end of block" } )
  assert_equal( "end of block",  iterate { "end of block" } )
end

I understand that Procs ( Which is what blocks are ) should return within the scope they are called. ( Unlike lambdas ) With this in mind, shouldn't both calls in the tests return "end of block"?

This test passes on 'ruby 1.8.7 (2009-06-12 patchlevel 174) [universal-darwin10.0]' ( OSX 10.6.7 )

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無心 2024-11-09 16:19:45

return 关键字从词法封闭方法返回。即*test_iterate*。

要以动态范围的方式从块返回特定值，您应该使用 break 关键字。

对于您的情况：

iterate { break("end of block") }

测试将失败。因为 iterate 方法的第二个 return 语句永远不会运行。

预期的语义应该通过使用异常来完成：

def iterate
  return yield
  rescue :exception
    return "end of iterate"
end

def test_iterate
  assert_equal( "end of iterate",  iterate { raise :exception } )
  assert_equal( "end of block",  iterate { "end of block" } )
end

The return keyword returns from the lexicaly enclosing method. That is, *test_iterate*.

To return a certain value from a block in a dynamically scoped fashion, you should use the break keyword instead.

In your case:

iterate { break("end of block") }

The test will fail. because the second return statement of the iterate method will never run.

The intended semantics should be accomplished by using exceptions:

def iterate
  return yield
  rescue :exception
    return "end of iterate"
end

def test_iterate
  assert_equal( "end of iterate",  iterate { raise :exception } )
  assert_equal( "end of block",  iterate { "end of block" } )
end

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