Issue #16260 has been updated by mame (Yusuke Endoh).

Target version set to 2.8
Assignee set to nobu (Nobuyoshi Nakada)
Tracker changed from Misc to Feature

At the previous meeting, matz said it should return true.  Will do.

----------------------------------------
Feature #16260: Symbol#to_proc behaves like lambda, but doesn't aknowledge it
https://bugs.ruby-lang.org/issues/16260#change-83409

* Author: zverok (Victor Shepelev)
* Status: Open
* Priority: Normal
* Assignee: nobu (Nobuyoshi Nakada)
* Target version: 2.8
----------------------------------------
Seems that `Symbol#to_proc` returns `Proc` that has lambda semantics:
```ruby
proc = :+.to_proc
proc.call(1, 2)   # => 3
proc.call([1, 2]) # ArgumentError (wrong number of arguments (given 0, expected 1))
```
But if you ask...
```ruby
proc.lambda? # => false
```

That seems to be an inconsistency, which I'd like to clarify. There are obviously two ways to fix it:
1. Make it respond `true` to `lambda?` (and mention the semantics in docs)
2. Make it behave like non-lambda.

The second one seems to produce some useful behavior:
```ruby
# Currently:
[1, 2].zip([3, 4]).map(&:+) # ArgumentError (wrong number of arguments (given 0, expected 1))

# With non-lambda:
class Symbol
  def to_proc
    proc { |o, *a| o.send(self, *a) }
  end
end

[1, 2].zip([3, 4]).map(&:+) # => [4, 6] 
```

Probably all of it was discussed when `Symbol#to_proc` was introduced, but as old NEWS-files doesn't link to tickets/discussions, I can't find the reasoning for current behavior.



-- 
https://bugs.ruby-lang.org/

Unsubscribe: <mailto:ruby-core-request / ruby-lang.org?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>