Add Support for Non-Symbol Keyowrds
(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 asdef add_one: (0 => Integer). -
**<type> => <type>, such asdef 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