From: "tenderlovemaking (Aaron Patterson) via ruby-core" <ruby-core@...>
Date: 2023-12-05T19:52:33+00:00
Subject: [ruby-core:115593] [Ruby master Bug#20041] Array destructuring and default values in parameters

Issue #20041 has been reported by tenderlovemaking (Aaron Patterson).

----------------------------------------
Bug #20041: Array destructuring and default values in parameters
https://bugs.ruby-lang.org/issues/20041

* Author: tenderlovemaking (Aaron Patterson)
* Status: Open
* Priority: Normal
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
It's possible to set the default value of a parameter to a previous parameter.  For example:

```ruby
def foo(a, b = a)
  b
end

foo([1, 2]) # => [1, 2]
```

However, if the parameters are destructured, the destructring happens _after_ default parameter assignment.  For example:

```ruby
def foo((x, y), b = x)
  [x, y, b]
end

foo([1, 2]) # => [1, 2, nil]
```

Is this expected behavior?  I would have expected the parameters to be "evaluated" from left to right, and the array destructuring to happen _before_ the default parameter assignment.

Thanks!



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