Feature #21813: Add [:forward, :...] symbol tuple to indicate forwarding arguments when calling `Method#parameters`

• Status: Rejected
• Assignee: -
• Target version: -

[pabloh (Pablo Herrero)]

When accessing Method#parameters for a method using forwarding parameters, an unexpected behavior arises:

def foo(*, **, &)
  args = method(__method__).parameters.map(&:last).join(',')

  binding.eval "print(#{args})" # Works fine
end

foo(1,2,3,4, a: 23) # => 1234{a: 23}

def bar(...)
  args = method(__method__).parameters.map(&:last).join(',') 

  binding.eval "print(#{args})" # Fails!
end

bar(1,2,3,3, a: 23) # SyntaxError

It's very strange that you can't access the parameters, on eval, using the symbols provided at Method#parameters.

Adding [:forward, :...] or [:forwarding, :...] for those cases feels simply natural.

[pabloh (Pablo Herrero)]

• Description updated (diff)

[pabloh (Pablo Herrero)]

• Description updated (diff)

[pabloh (Pablo Herrero)]

• Description updated (diff)

[pabloh (Pablo Herrero)]

• Description updated (diff)

[nobu (Nobuyoshi Nakada)]

foo(a: 1) doesn't print what you expect, I guess.

[pabloh (Pablo Herrero)]

@nobu (Nobuyoshi Nakada) Perhaps I came up with a contrived example, but I wanted to point out that there is a lack of symmetry when it comes to ...
As of right now, there is no way to know from the Method reflection API alone whether a method is using argument forwarding. You’d have to use Method#source_location and then parse the source file somehow.

EDIT: I updated the example for better clarity, but the main point remains the same: the lack of an introspection API for argument forwarding.

[pabloh (Pablo Herrero)]

• Description updated (diff)

[matz (Yukihiro Matsumoto)]

• Status changed from Open to Rejected

I failed to persuade me. I admit there's a lack of symmetry, but I don't think it's not worth the potential performance burden.

Matz.