Feature #20318
Updated by bradgessler (Brad Gessler) 2 months ago
# 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:, kwargs:, 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"
```
Or an array like this:
```ruby
def bar(*args, **kwargs, &block)
case [args, kwargs, block]
in [name], {}, nil
puts name
in [first_name, last_name], {}, nil
puts "Hi there #{first_name} #{last_name}"
in [], {greeting:}, nil
puts "Hello #{greeting}"
else
puts "No match: #{args}, #{kwargs}"
end
end
bar "Howdy"
bar "Bradley", "Gessler"
bar greeting: "Bradley"
```
# 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.
The array would look like this:
```ruby
def bar(...)
case ...
in [name], {}, nil
puts name
in [first_name, last_name], {}, nil
puts "Hi there #{first_name} #{last_name}"
in [], {greeting:}, nil
puts "Hello #{greeting}"
else
puts "No match: #{args}, #{kwargs}"
end
end
bar "Howdy"
bar "Bradley", "Gessler"
bar greeting: "Bradley"
```