ruby-core

Issue #19633 has been updated by shioyama (Chris Salzberg).


> The question was: If `/foo` is a root directory, and you want to associate to it an anonymous module as custom namespace, how would `/foo/bar.rb` look like?

Sorry, I read your comment too quickly. I actually removed the entire concept of a custom namespace in Im because it doesn't really feel useful once the root is anonymous (see [this commit](https://github.com/shioyama/im/commit/1eca0c202c51e1ee74243d19e575bd514879ae19)).

So, I answered the wrong question, but hopefully my answer is useful anyway!

----------------------------------------
Feature #19633: Allow passing block to `Kernel#autoload` as alternative to second `filename` argument
https://bugs.ruby-lang.org/issues/19633#change-103064

* Author: shioyama (Chris Salzberg)
* Status: Open
* Priority: Normal
----------------------------------------
`Kernel#autoload` takes two arguments, a symbol `module` representing the constant to be autoloaded, and a `filepath` to load the constant from (with `require`).

Currently, Zeitwerk has to [monkeypatch `Kernel#require`](https://github.com/fxn/zeitwerk/blob/a7c4a983df0f4e4058f32c610dac1e8b99f687da/lib/zeitwerk/kernel.rb) to fetch the loader for the file being loaded, then run the original (aliased) `require`, then run autoload callbacks. In addition to the monkeypatch, this also requires a registry (`Zeitwerk::Registry`) to map file paths to loaders, to know which loader should be used for a given autoload-triggered `require`. In fact, Zeitwerk has to _assume_ that the monkey-patched `require` call came from an autoload trigger; there is no way to really be sure of the source.

If Ruby allowed passing a block as an alternative to the explicit filepath, then I think this could be improved and would eliminate the need for a monkeypatch. So something like this:

```ruby
autoload(:B) do
  require "lib/b"
  # trigger callback, etc
end
```

I am implementing a gem called [Im](https://github.com/shioyama/im) which is a fork of Zeitwerk, and in the case of this gem, such a feature would be even more useful. Im implements autoloads on anonymous modules by registering an autoload and then "catching" the require and converting it into a `load`, passing the module as the second argument (see [here](https://github.com/shioyama/im/blob/44ce348639a1aae563a5be7a40602761e9698d43/lib/im/kernel.rb).) This is currently quite tricky because, again, it's hard to know _where_ a `require` came from.

In addition to removing the monkeypatch (inherited from Zeitwerk), Im would further benefit from the block argument because then it could simply access the module via a closure, rather than pulling it from a registry:

```ruby
mod.autoload(:Foo) do
  load "lib/foo.rb", mod
end
```

I don't know how hard or easy this would be to implement, but if there is interest in this as a feature I'd be happy to look into implementing it.



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