Ruby: 隐式块转换为 Proc

Question

我的理解是必须生成隐式附加到方法的块；它不能被调用。所以我试图理解为什么会这样：

def execute_code
  proc.call
end

execute_code { "Why does this work?" } # => "Why does this work?"

将块附加到此代码成功执行。

有什么见解吗？我还没有找到任何文档暗示隐式块会自动转换为 proc 对象并分配给变量 proc.

Ruby 2.5.3

Answer 1

对于 Ruby 2.5.3，docs for Kernel#proc() 表示：

Equivalent to Proc.new.

和 docs for Proc.new 说：

Creates a new Proc object, bound to the current context. Proc::new may be called without a block only within a method with an attached block, in which case that block is converted to the Proc object.

这就是您的示例中发生的情况。您在带有块的方法中调用 proc，并且该块正在转换为 Proc.

但是，此行为在更高版本中发生了变化。如果你在 Ruby 2.7,1 中尝试，你会收到这样的警告（尽管它仍然有效）：

proc.rb:2: warning: Capturing the given block using Kernel#proc is deprecated; use `&block` instead

在 Ruby 3 中，它根本不起作用（实际上表现如您所料）：

proc.rb:2:in `proc': tried to create Proc object without a block (ArgumentError)
    from proc.rb:2:in `execute_code'
    from proc.rb:5:in `<main>'

docs for 3.0.0 are unchanged though. This looks like a bug in the docs (it has been fixed in master). It looks like this was first raised in the issue tracker in 2014 and then later in 2019.

Ruby: 隐式块转换为 Proc

Ruby: Implicit Block Converted to Proc

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anonymous-function

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