[ruby-core:117021] [Ruby master Feature#20318] Pattern matching `case ... in` support for triple-dot arguments

Issue #20318 has been reported by bradgessler (Brad Gessler).

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Feature #20318: Pattern matching `case ... in` support for triple-dot arguments
https://bugs.ruby-lang.org/issues/20318

* Author: bradgessler (Brad Gessler)
* Status: Open
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# Premise

Sometimes when I'm creating a method for an API, I'd like to do pattern matching against the arguments. Today I have to do something like this:

```ruby
def foo(*args, **kwargs, &block)
  case { args: args, kwargs: kwargs, block: block }
    in args: [name]
      puts name
    in args: [first_name, last_name]
      puts "Hi there #{first_name} #{last_name}"
    in kwargs: {greeting:}
      puts "Hello #{greeting}"
    else
      puts "No match: #{args}"
  end
end

foo "Hi"
foo "Brad", "Gessler"
foo greeting: "Brad"
```

# Proposal

I'd like to propose the same thing, but for `...`, like this:

```ruby
def foo(...)
  case ...
    in args: [name]
      puts name
    in args: [first_name, last_name]
      puts "Hi there #{first_name} #{last_name}"
    in kwargs: {greeting:}
      puts "Hello #{greeting}"
    else
      puts "No match: #{args}"
  end
end

foo "Hi"
foo "Brad", "Gessler"
foo greeting: "Brad"
```

One thing I'm not sure sure about: the `args`, `kwargs`, and `block` names appear out of thin air, so ideally those could somehow be named or have a syntax that doesn't require those names.



-- 
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