ruby - Ruby 中 at_exit 和 END(大写)的区别

Question

Kernel#at_exit 之间存在哪些差异(如果有)方法和 END (全部大写)关键字？后者仅仅是一种更 Perlish 的做事方式，而前者更像 Ruby 吗？

我尝试执行 defined?(END {puts "Bye"})，但出现语法错误。

Answer 1

“The Ruby Programming Language”定义了它们行为上的细微差别。 at_exit 可以在循环中多次调用，每次迭代调用都将在代码退出时执行。 END 只会在循环内调用一次。

...If an END statement is within a loop and is executed more than once, then the code associated with it is still only registered once:

a = 4;
if (true)
  END { # This END is executed
  puts "if"; # This code is registered
  puts a # The variable is visible; prints "4"
}
else
  END { puts "else" } # This is not executed
end
10.times {END { puts "loop" }} # Only executed once

The Kernel method at_exit provides an alternative to the END statement; it registers a block of code to be executed just before the interpreter exits. As with END blocks, the code associated with the first at_exit call will be executed last. If the at_exit method is called multiple times within a loop, then the block associated with it will be executed multiple times when the interpreter exits.

所以，运行:

2.times {
  END { puts 'END'}
  at_exit { puts 'at_exit' }
}

结果:

at_exitat_exitEND