Sorbet asking a `sig` for `attr_reader`

Question

Sorbet is showing an error for the attr_reader, but correct me if I am wrong, sigs are required when the function is declared, not called, right?

I have tried going through the documentation but all I got is this note

Note: Many Ruby constructs that look like local variables are actually method calls without parens! Specifically, watch out for attr_reader and zero-argument method definitions.

app/util/hodor.rb:125: This function does not have a `sig` https://sorbet.org/docs/error-reference#7017
     125 |  attr_reader(:collection_name)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Vidar

Where does this line of code appear? They normally are contained in class or module definitions. – Impulsive

Hm, sorbet playground doesn't give this error – Adaadabel

This error is silenced in all strictness levels below # typed: strict. The playground defaults to # typed: true if no sigil is given. In all other places Sorbet defaults to # typed: false if no sigil is given. sorbet.org/docs/static – Passion

Answer 1

The error does not have to do with the attr_reader method itself needing a sig, but with :collection_name. The signature for attr_reader is already known, but the new method it dynamically creates, #collection_name does not have a known sig, and Sorbet expects this to be the place where you give it one.

You can do this to fix it:

sig { returns(String) }
attr_reader(:collection_name)

Andesite

Is it correct that an attr_reader that defines multiple attributes will have to be split up over multiple lines to make the signatures work correctly? – Gird

Answer 2

attr_reader(attribute) is the equivalent of :

def attribute
  @attribute
end

This is probably why Sorbet is asking for a sig.

Peekaboo

Answer 3

Here's the Sorbet documentation on it:

It goes something like this:

# typed: true
class A
  extend T::Sig

  sig {returns(Integer)}
  attr_reader :reader

  sig {params(writer: Integer).returns(Integer)}
  attr_writer :writer

  # For attr_accessor, write the sig for the reader portion.
  # (Sorbet will use that to write the sig for the writer portion.)
  sig {returns(Integer)}
  attr_accessor :accessor

  sig {void}
  def initialize
    @reader = T.let(0, Integer)
    @writer = T.let(0, Integer)
    @accessor = T.let(0, Integer)
  end
end

Stays