COMEFROM control flow

According to wikipedia COMEFROM flow control is considered a joke, unreadable or downright harmful. I'd imagine such a feature would be very useful in AOP scenarios (ie. adding logger to methods without adding logger calls to methods).

Does the downside of non-obviousness of such a contro开发者_开发百科l structure outweigh the potential usefulness? Are there any other downsides to consider?

Prompted to ask this question because of this.

---

For starters is basically useless in any modern language because you need to either:

• Reference the position to jump from by line number, and these are volatile.
• Place a marker or label in the code to denote a position that can be jumped from, thus destroying any possible benefits of not needing to do this.

Also:

• Makes any kind of debugging by inspection essentially useless.
• Can't really capture any context from where it jumped unless you keep variables persistant, which is asking for trouble.

A much better idea would be to instead:

• Write a hooking API.
• Call a function!

---

For the purpose you mention, Aspect Oriented Programming (wikipedia) seems a more organized solution than comefrom. See the bottom of Motiviation and Basic Concepts (ibid) for an example of how logging can be added to a method in a separate textual unit.

In a sufficiently dynamic language, it is possible to handle this sort of thing using "wrap-around" modifiers to a method:

  def do_something
    ...
  end
  log :do_something, "Something got done"

In this contrived example, the log macro causes the do_something method to be replaced by a new method which first calls the original do_something method, and then writes something to the log.