Ability to typedef a proc that can accept variable amount of params

[hdoan741]

Problem

I'd like to typedef a proc that can accept variable amount of params

-> View on sorbet.run

# typed: true

class District::Relation
  extend T::Sig
end

module District::ClassMethods
  extend T::Sig

  sig { 
    params(
      name: Symbol, 
      body: T.proc.params(args: T.untyped).returns(T.untyped), 
      block: T.nilable(T.proc.void)
    ).void
  }
  def scope(name, body, block=nil); end
end

class District
  extend T::Sig
  extend District::ClassMethods

  scope :no_param, -> {
  }

  scope :two_params, -> (a, b) {
  }
end

Output

editor.rb:24: T.proc.returns(T.untyped) does not match T.proc.params(arg0: T.untyped).returns(T.untyped) for argument body https://srb.help/7002
    24 |  scope :no_param, -> {
    25 |  }
    editor.rb:13: Method District::ClassMethods#scope has specified body as T.proc.params(arg0: T.untyped).returns(T.untyped)
    13 |      body: T.proc.params(args: T.untyped).returns(T.untyped), 
              ^^^^
  Got T.proc.returns(T.untyped) originating from:
    editor.rb:24:
    24 |  scope :no_param, -> {
    25 |  }

Proposed solution

Something like that should be typecheck-able. In terms of API, there are several options:

T.proc.params(*a: T.untyped).void
T.proc.params(a: T.rest[T.untyped]).void

[hdoan741]

It seems to work for an explicit block (sorbet.run link) but not a lambda (sorbet.run link)

(However, calling the block with variable number of argument would trigger error still, so maybe it's still the same)

[pje]

Variadic procs are kinda fake-able by typedefing a T.any that just enumerates all the possible arities of the function: sorbet.run link

(Interestingly there appears to be a hard-coded limit of 10 args for all proc sigs.)

FWIW, this is kinda like what Scala does under the hood for variadic function types—their stdlib literally has Function1.scala through Function22.scala: https://github.com/scala/scala/blob/d46849d2b77fdc710fc00611e225ba371475a65a/src/library/scala/Function22.scala#L18

[hdoan741]

The thing with T.any is that it doesn’t work with T.proc.bind, which is almost required to type any Rails thing properly.

…

On Sat, Jun 29, 2019 at 11:01 AM Patrick Ellis ***@***.***> wrote: It's fake-able with a typedef and a T.any that just enumerates all the possible forms of the variadic function: https://sorbet.run/#%23%20typed%3A%20true%0A%0Aclass%20District%3A%3ARelation%0A%20%20extend%20T%3A%3ASig%0Aend%0A%0AVariadicUntypedProc%20%3D%20T.type_alias(%0A%20%20T.any(%0A%20%20%20%20T.proc.returns(T.untyped)%2C%0A%20%20%20%20T.proc.params(arg0%3A%20T.untyped).returns(T.untyped)%2C%0A%20%20%20%20T.proc.params(arg0%3A%20T.untyped%2C%20arg1%3A%20T.untyped).returns(T.untyped)%2C%0A%20%20%20%20T.proc.params(arg0%3A%20T.untyped%2C%20arg1%3A%20T.untyped%2C%20arg2%3A%20T.untyped).returns(T.untyped)%2C%20%0A%20%20%20%20T.proc.params(arg0%3A%20T.untyped%2C%20arg1%3A%20T.untyped%2C%20arg2%3A%20T.untyped%2C%20arg3%3A%20T.untyped).returns(T.untyped)%2C%0A%20%20%20%20T.proc.params(arg0%3A%20T.untyped%2C%20arg1%3A%20T.untyped%2C%20arg2%3A%20T.untyped%2C%20arg3%3A%20T.untyped%2C%20arg4%3A%20T.untyped).returns(T.untyped)%2C%0A%20%20%20%20T.proc.params(arg0%3A%20T.untyped%2C%20arg1%3A%20T.untyped%2C%20arg2%3A%20T.untyped%2C%20arg3%3A%20T.untyped%2C%20arg4%3A%20T.untyped%2C%20arg5%3A%20T.untyped).returns(T.untyped)%2C%0A%20%20%20%20T.proc.params(arg0%3A%20T.untyped%2C%20arg1%3A%20T.untyped%2C%20arg2%3A%20T.untyped%2C%20arg3%3A%20T.untyped%2C%20arg4%3A%20T.untyped%2C%20arg5%3A%20T.untyped%2C%20arg6%3A%20T.untyped).returns(T.untyped)%2C%0A%20%20%20%20T.proc.params(arg0%3A%20T.untyped%2C%20arg1%3A%20T.untyped%2C%20arg2%3A%20T.untyped%2C%20arg3%3A%20T.untyped%2C%20arg4%3A%20T.untyped%2C%20arg5%3A%20T.untyped%2C%20arg6%3A%20T.untyped%2C%20arg7%3A%20T.untyped).returns(T.untyped)%2C%0A%20%20%20%20T.proc.params(arg0%3A%20T.untyped%2C%20arg1%3A%20T.untyped%2C%20arg2%3A%20T.untyped%2C%20arg3%3A%20T.untyped%2C%20arg4%3A%20T.untyped%2C%20arg5%3A%20T.untyped%2C%20arg6%3A%20T.untyped%2C%20arg7%3A%20T.untyped%2C%20arg8%3A%20T.untyped).returns(T.untyped)%2C%0A%20%20%20%20T.proc.params(arg0%3A%20T.untyped%2C%20arg1%3A%20T.untyped%2C%20arg2%3A%20T.untyped%2C%20arg3%3A%20T.untyped%2C%20arg4%3A%20T.untyped%2C%20arg5%3A%20T.untyped%2C%20arg6%3A%20T.untyped%2C%20arg7%3A%20T.untyped%2C%20arg8%3A%20T.untyped%2C%20arg9%3A%20T.untyped).returns(T.untyped)%0A%20%20)%0A)%0A%0Amodule%20District%3A%3AClassMethods%0A%20%20extend%20T%3A%3ASig%0A%0A%20%20sig%20%7B%20%0A%20%20%20%20params(%0A%20%20%20%20%20%20name%3A%20Symbol%2C%20%0A%20%20%20%20%20%20body%3A%20VariadicUntypedProc%2C%20%0A%20%20%20%20%20%20block%3A%20T.nilable(T.proc.void)%0A%20%20%20%20).void%0A%20%20%7D%0A%20%20def%20scope(name%2C%20body%2C%20block%3Dnil)%3B%20end%0Aend%0A%0Aclass%20District%0A%20%20extend%20T%3A%3ASig%0A%20%20extend%20District%3A%3AClassMethods%0A%0A%20%20scope%20%3Ano_param%2C%20-%3E%20%7B%7D%0A%20%20scope%20%3Aone_param%2C%20-%3E%20(a)%20%7B%7D%0A%20%20scope%20%3Atwo_params%2C%20-%3E%20(a%2C%20b)%20%7B%7D%0A%20%20scope%20%3Athree_params%2C%20-%3E%20(a%2C%20b%2C%20c)%20%7B%7D%0Aend%0A (Also there appears to be a hard-coded limit—procs can only take a maximum of 9 args.) — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#1142?email_source=notifications&email_token=AAFH4AIKW7STHZ5GPOBKO2LP46PQLA5CNFSM4H4JQUR2YY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGODY35NHI#issuecomment-506975901>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAFH4ALOHZJVMST42WZDM5DP46PQLANCNFSM4H4JQURQ> .

[searls]

👍 This would be terrific and allow Mocktail to specify the type of block parameters when we don't know anything about the block other than the fact that it's a block. In Mocktail's internal T::Struct value that tracks calls to faked methods, I've had to settle for the prop block: T.nilable(T.anything) for whether the invocation took a block