Skip to content

Add Support for Non-Symbol Keyowrds #1645

Description

@sampersand

(Originally posted as a discussion, #1609, I think this is better as an issue)

While working on Kernel#system, I came across a limitation of RBS: it only lets you specify symbol keyword arguments, and not any other type.

Normal keyword arguments in Ruby are passed via key: value, such as gets(chomp: true). However, this syntax is actually sugar for gets(:chomp => true), and Ruby is capable of accepting other values for keys.

Take this contrived example:

def add_one(**kw)
  raise ArgumentError, "missing `0`" unless kw.key?(0)
  raise ArgumentError, "unknown keywords: #{kw.keys - [0]}" unless kw.keys == [0]
  kw[0] + 1
end
p add_one(0 => 3) #=> 4

Or this slightly-less-contrived example:

def add_exponentiated_numbers(**kwargs)
  sum = 0
  kwargs.each do |key, value|
    sum += key ** value
  end
end

puts add_exponentiated_numbers 2=>3, 4=>5, 6=>7 #=> 280968

There's no real way to typecheck this currently in RBS, as RBS only supports symbols for hash keys. It does have a **rest parameter, but that expects symbols as hash keys as well.

I propose we add two new pieces of syntax to function declarations:

  • <literal> => <type>, such as def add_one: (0 => Integer).
  • **<type> => <type>, such as def add_exponentiated_numbers: (**Integer => Integer).

Notably, the ** variant isn't equivalent (nor replaces) the current **<type> <variable> syntax. For example, a simplified Kernel#system (which can take integers for hash keys, which correspond to hash descriptors) could be defined as:

def system: (String cmd, **Integer => Integer, **untyped other_options) -> bool

Activity

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Metadata

Metadata

Assignees

No one assigned

    Labels

    No labels
    No labels

    Type

    No type

    Projects

    No projects

      Milestone

      No milestone

      Relationships

      None yet

      Development

      No branches or pull requests

      Issue actions