In Ruby, why is it not enough to alias `method_missing` to catch call to undefined methods?

Question

That seems all the more unexpected when defining a dummy method passing all arguments do the job. That is the following works:

  def method_missing(ago, *lokatoj, &bloko)
    mistrafe(ago, *lokatoj, &bloko)
  end

  def mistrafe(ago, *lokatoj, &bloko)
    # faru ion
  end

While the following doen't

alias mistrafe method_missing

Why is that so?

Why don't you move the implementation into `method_missing`? — Stefan, Jul 03 '18 at 10:47

score 4 · Accepted Answer · edited Jul 03 '18 at 08:16

4

Generally speaking, you want method_missing (that is called by Ruby internally) to be an alias for mistrafe not vice versa. You have an implementation in mistrafe and you want reassign method_missing to be calling it.

That said, the following will work:

alias method_missing mistrafe

See the alias documentation.

edited Jul 03 '18 at 08:16

3limin4t0r

19,353
2
31
52

answered Jul 03 '18 at 08:08

Aleksei Matiushkin

119,336
10
100
160

Yes, it works. I'm astonished with my own confusion as with other methods aliases, I didn't made this error of inverting parameters. Now to be complete, for some reason in this case it seems required to put the alias *after* the method definition, when I can successfully alias other methods before there definition. Any idea why is that so? – psychoslave Jul 03 '18 at 08:34
Use [`Module#alias_method`](https://ruby-doc.org/core/Module.html#method-i-alias_method) to put it wherever. `alias` requires the method to exist due to it’s syntax. – Aleksei Matiushkin Jul 03 '18 at 08:36
1

But before you use `alias_method` over `alias`, first have a look at the differences and decide for yourself. https://stackoverflow.com/a/27310250/3982562 – 3limin4t0r Jul 03 '18 at 09:40
Understandably, `alias` can't be aliased as it's a language keyword, and no keyword can be aliased. But shouldn't it possible to alias `alias_method`? I tried to make `alias alivoke alias_method` and ended with `undefined method `alias_method' for module `Ĝue' (NameError)` – psychoslave Jul 03 '18 at 12:41
class Module alias_method :alivoke, :alias_method ;end – psychoslave Jul 03 '18 at 13:07
Thus said, @mudasobwa and @johan-wentholt even with `alias_method` it only works if it's placed after the `mistrafe` method. – psychoslave Jul 04 '18 at 02:59

In Ruby, why is it not enough to alias `method_missing` to catch call to undefined methods?

1 Answers1