[ruby-core:71353] [Ruby trunk - Feature #11660] [Open] a falsy value (similar to js undefined) that facilitates forwarding of default arguments

Issue #11660 has been reported by bug hit.

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Feature #11660: a falsy value (similar to js undefined) that facilitates forwarding of default arguments
https://bugs.ruby-lang.org/issues/11660

* Author: bug hit
* Status: Open
* Priority: Normal
* Assignee: 
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I'll call it "missing" here.  Consider the following scenario:

```ruby
def foo(default1 = some_expression)
end

def bar(default1 = some_expression)
  foo default1
end

def foobar(default1 = some_expression)
  bar default1
end 
```

if you had "missing":

```ruby
def foo(default1 = some_expression)
end

def bar(default1 = missing)
  foo default1
end

def foobar(default1 = missing)
  bar default1
end 
```
missing passed as arg would be ignored (as if it wasn't passed at all)
and you wouldn't have to repeat the default value expression in every method

I believe that's how undefined works in js6 with respect to default args 




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