[ruby-core:117069] [Ruby master Feature#20318] Pattern matching `case ... in` support for triple-dot arguments
From:
"ntl (Nathan Ladd) via ruby-core" <ruby-core@...>
Date:
2024-03-06 20:10:18 UTC
List:
ruby-core #117069
Issue #20318 has been updated by ntl (Nathan Ladd).
It might be a good idea to consider how proc/lambda/block arguments could also have comparable syntax. For instance, a block argument example:
``` ruby
HTTP.post("http://example.com/some-resource", "some data") do |...|
in code: (200...300)
puts "Success!"
in code: (300...400), location:
puts "Redirect to #{location}"
# post to location
in code: (500...600)
puts "Server error"
do_retry
end
```
----------------------------------------
Feature #20318: Pattern matching `case ... in` support for triple-dot arguments
https://bugs.ruby-lang.org/issues/20318#change-107142
* Author: bradgessler (Brad Gessler)
* Status: Open
----------------------------------------
# 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:, 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"
```
--
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