[ruby-core:74858] [Ruby trunk Feature#12262] Anti-loop

Issue #12262 has been updated by Robert A. Heiler.


I don't have any big pro or contra opinion, but there is one thing I am wondering:

Is this still called a loop in the second case? Because the default is to break 
after the first run. And a loop implies to continue, until one ends it or? :-)

However had, what I might find interesting, is to have other means to force the
end of a loop. Like, "break" is used, but what if we could designate another
way to end a loop? If we could do that, then perhaps your suggestion might be
implied to work in the second case, because you could somehow specify that
loop would en when a "return nil" would be implied.

E. g. something like (the syntax does not work, it just is an example):

    loop(break_on: nil) {
      if ...
        ...
      elsif ...
        ...
      elsif ...
        ...
        next # continues on exceptional cases
      else
        ...
      end
    }   

Where the default would be a loop like:


    loop(break_on: :break)

Which can be omitted. (The symbol :break would then default on the
keyword break).

Please consider this just as food-for-thought, I actually do not
really suggest it - I am just playing with the thought here. :)

(I myself probably would prefer "the simpler, the better" which
is why I do not suggest a change, but as said, I am neutral on
this suggestion.)

----------------------------------------
Feature #12262: Anti-loop
https://bugs.ruby-lang.org/issues/12262#change-57986

* Author: Tsuyoshi Sawada
* Status: Open
* Priority: Normal
* Assignee: 
----------------------------------------
The `loop` method continues by default, and requires the keyword `break` to escape. This is good when the continuing cases are the norm and the escaping cases are exceptional:

~~~RUBY
loop do
  ...
  if ...
    ...
  elsif ...
    ...
  elsif ...
    ...
    break # breaks on exceptional cases
  elsif ...
    ...
  else
    ...
  end
end
~~~

But when the continuing cases are exceptional and the escaping cases are the norm, the construction requires a lot of `break`, and it becomes cumbersome:

~~~RUBY
loop do
  ...
  if ...
    ...
    break # lot of breaks
  elsif ...
    ...
    break # lot of breaks
  elsif ...
    ...
    break # lot of breaks
  elsif ...
    ...
  else
    ...
    break # lot of breaks
  end
end
~~~

I actually see this use case a lot when user input is asked with validation on a command line script.

I request a `loop`-like method that works in the opposite way to `loop`, that is, it escapes (i.e., runs only once) by default, and requires a keyword to continue (perhaps `next`). The second code above would then be written like:

~~~RUBY
some_loop_like_method do
  ...
  if ...
    ...
  elsif ...
    ...
  elsif ...
    ...
  elsif ...
    ...
    next # continues on exceptional cases
  else
    ...
  end
end
~~~




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