basics/hash_and_array_constructors_no_parens.rb

tests/_examples/basics/hash_and_array_constructors_no_parens.rb in the metorex repository.

# `Hash[]` reads a list of pairs, a hash, or one argument that answers
# `to_hash` or `to_ary`, and refuses an element that names no pair.
p Hash[[[:a, :b], [:c, :d]]]
p Hash[[[:a]]]
begin
  Hash[[:a]]
rescue ArgumentError => refused
  p refused.message
end
begin
  Hash[[[:a, :b, :c]]]
rescue ArgumentError => refused
  p refused.message
end

class Pairs
  def to_ary
    [[:a, :b]]
  end
end
p Hash[Pairs.new]

# `Array.new` given an array takes its elements rather than a size, and
# refuses a default alongside one.
p Array.new([4, 5, 6])

class Listed
  def to_ary
    [1, 2]
  end
end
p Array.new(Listed.new)
begin
  Array.new([1, 2], 1)
rescue TypeError => refused
  p refused.class
end

Output:

{a: :b, c: :d}
{a: nil}
"wrong element type Symbol at 0 (expected array)"
"invalid number of elements (3 for 1..2)"
{a: :b}
[4, 5, 6]
[1, 2]
TypeError