Issue #17737 has been updated by marcandre (Marc-Andre Lafortune).


I am not opposed to changes, but I don't believe this actually matters; I can not think of a use-case.

A similar question could be asked of `[].permutation(:oops)`. Should it raise immediately? Asked another way, if the argument responds to `to_int`, should it be called immediately, or when iterated (or both)?

The ideal is probably that argument checking and conversion be done exactly once and when the enumerator is created, but I don't think it would make a different in the real world.



----------------------------------------
Bug #17737: `Array#permutation` does not immediately check the arity when no block is given
https://bugs.ruby-lang.org/issues/17737#change-91154

* Author: kachick (Kenichi Kamiya)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-darwin20]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
```ruby
p [].permutation(1) #=> #<Enumerator: []:permutation(1)>
p [].permutation(1, 3) #=> #<Enumerator: []:permutation(1, 3)>
p [].permutation(1, 3).to_a #=> `permutation': wrong number of arguments (given 2, expected 0..1) (ArgumentError)
```

```ruby
p [].cycle(1) #=> #<Enumerator: []:cycle(1)>
p [].cycle(1, 3) #=> `cycle': wrong number of arguments (given 2, expected 0..1) (ArgumentError)
```

Is this an intentional behavior?
I would expect `To raise ArgumentError immediately if the arity is wrong` like Array#cycle.

PR: https://github.com/ruby/ruby/pull/4267



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