[Proposal] Make`-> void` return type annotation on `initialize` methods to be implicit

[deepak-shopify]

I propose simplifying the RBS syntax for initialize methods by removing the required -> void return type annotation.

Current Syntax:

#: (a: String) -> void
def initialize(a:)
  @a = a
end

Proposed Syntax:

#: (a: String?)
def initialize(a:)
  @a = a
end

Why?

1. Redundant - I was moving from Sorbet sigs to RBS style sigs and noticed that I was adding the -> void to every initialize method. Even though it makes sense from a completeness perspective, it seemed redundant to me and does not add any new information.

2. Initialize is special - The initialize method is already special in Ruby - it's the only method that is called indirectly through new, cannot meaningfully return a value to its caller, has a fixed, unchangeable return behavior. Making its type signature special in RBS would accurately reflect its special status in the language.

3. Comparison with other languages:

   Language	Example	Requires Return Type?
   Python (with types)	def __init__(self, a: str):	Optional
   TypeScript	constructor(a: string) { }	No
   Java	public MyClass(String a) { }	No
   C#	public MyClass(string a) { }	No
   Go	N/A - uses factory functions instead	N/A
   Ruby (current RBS)	#: (a: String) -> void	Yes

[ParadoxV5]

👌 won’t hurt since RBS isn’t currently taking advantage of these round parentheses for a dedicated structure.

Edit: such as https://github.com/ruby/rbs/discussions/1639#discussioncomment-10153229? 🤔 Nah, they are compatible.