From: ko1@...
Date: 2019-01-16T10:12:46+00:00
Subject: [ruby-core:91121] [Ruby trunk Bug#15539] Proc.new with no block	shouldn't always warn

Issue #15539 has been updated by ko1 (Koichi Sasada).

Status changed from Open to Rejected

> makes it no longer possible to have a default value for a positional argument that uses the block

Surprisingly, we can:

```
def foo o = binding.local_variable_get(:b), &b
  p o.class
end

foo{} #=> Proc
```

(of course it is joke code. it is too implementation dependent code so we shouldn't rely on this behavior)

Anyway, I close this ticket and discuss more on new ticket I'll file.

Thanks,
Koichi

----------------------------------------
Bug #15539: Proc.new with no block shouldn't always warn
https://bugs.ruby-lang.org/issues/15539#change-76353

* Author: tenderlovemaking (Aaron Patterson)
* Status: Rejected
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
Hi,

r66772 introduced a warning for the following code:

``` ruby
def foo bar = Proc.new
  bar.call
end

foo      { p "block" } # warn
foo ->() { p "block" } # no warn
```

I don't think this case of `Proc.new` should warn.  To eliminate warnings, I have to rewrite as:

``` ruby
def foo bar = nil
  if bar
    bar.call
  else
    yield
  end
end
```

Rails uses this "Proc.new" trick here:

* https://github.com/rails/rails/blob/a08827a90b5a9be79379019cf5b242bd7236d2e3/actionpack/lib/action_controller/metal.rb#L29
* https://github.com/rails/rails/blob/a08827a90b5a9be79379019cf5b242bd7236d2e3/actionpack/lib/action_dispatch/middleware/stack.rb#L100
* https://github.com/rails/rails/blob/a08827a90b5a9be79379019cf5b242bd7236d2e3/activerecord/lib/active_record/statement_cache.rb#L116
* https://github.com/rails/rails/blob/a08827a90b5a9be79379019cf5b242bd7236d2e3/activesupport/lib/active_support/notifications/fanout.rb#L21

I can change Rails, but I want to know why and I don't see any discussion of r66772 (the commit doesn't have a feature number).

Thanks!



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