Passing named arguments and variable number of arguments in block call

Question

I have a piece of test code:

def asdf(id: nil, field: nil, state: nil)
  puts "id: #{id}, field: #{field}"
end

def test(a, b, *args)
  # a, b are needed only inside #test
  yield(state: :created, *args)
end

test('a', 'b', id: 'xyz', field: :asd) { |*args| asdf(*args) }

It generates a syntax error:

syntax error, unexpected *
yield(state: :created, *args)

What is the correct way to call a block with a named parameter and an argument list? What is the idiomatic way to do this?

I also tried passing &block to test and doing block.call(state: :created, *args) with no luck.

Aleksei Matiushkin · Accepted Answer · 2015-09-25 07:12:27Z

3

You mixed up splat and double splat (note, that I changed all *args to **args):

def asdf(id: nil, field: nil, state: nil)
  puts "id: #{id}, field: #{field}"
end

def test(a, b, **args)
  # a, b are needed only inside #test
  yield(state: :created, **args)
end

test('a', 'b', id: 'xyz', field: :asd) { |**args| asdf(**args) }
#⇒ id: xyz, field: asd

Splat is used for unknown amount of plain params:

def test a, b, *args
  puts args.inspect
end
test 42, true, 'additional'
#⇒ ["additional"]

Double splat, introduced in Ruby2, is used to receive hash (named params):

def test a, b, **args
  puts args.inspect
end
test 42, true, hello: 'world'
#⇒ {:hello=>"world"}

answered Sep 25, 2015 at 7:12

Aleksei Matiushkin

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1 Comment

sawa Over a year ago

You are correct about the OP's mistake. But to be precise, that is not the direct cause of the syntax error (it would only cause an argument error). The reason for the syntax error is because named parameter (state: :created) was placed before *. However, what you pointed out is the indirect cause of the error.

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