Example of making an arg parser from a lambda signature https://twitter.com/josh_cheek/status/1364729672492277762

example.rb

# Example works if done in args instead of local var assignment:
-> a, b=nil, c { {a: a, b: b, c: c} }[1, 2] # => {:a=>1, :b=>nil, :c=>2}

# Lib could, eg reflect on param types
def arg_parser(&block)
  lambda do |argv|
    argv, args = argv.dup, []
    keywords = block.parameters.filter_map { |t, n| [n, false] if t == :keyreq }.to_h
    while (arg = argv.shift)
      next args << arg unless /^--?(.*)/ =~ arg
      keywords[$1.intern] = argv[0] !~ /^[^-]/ || argv.shift
    end
    block.call(*args, **keywords)
  end
end

parse = arg_parser &-> a, b='_', *ords, d: '_', e:, bool:, **keys do
  {a:a, b:b, d:d, e:e, bool:bool, ords:ords, keyrest: keys}
end

parse.call %w[a -e e]         # => {:a=>"a", :b=>"_", :d=>"_", :e=>"e", :bool=>false, :ords=>[], :keyrest=>{}}
parse.call %w[a b -e e]       # => {:a=>"a", :b=>"b", :d=>"_", :e=>"e", :bool=>false, :ords=>[], :keyrest=>{}}
parse.call %w[a b c1 -e e]    # => {:a=>"a", :b=>"b", :d=>"_", :e=>"e", :bool=>false, :ords=>["c1"], :keyrest=>{}}
parse.call %w[a b c1 c2 -e e] # => {:a=>"a", :b=>"b", :d=>"_", :e=>"e", :bool=>false, :ords=>["c1", "c2"], :keyrest=>{}}
parse.call %w[a -d d -e e]    # => {:a=>"a", :b=>"_", :d=>"d", :e=>"e", :bool=>false, :ords=>[], :keyrest=>{}}
parse.call %w[a -e e -d d]    # => {:a=>"a", :b=>"_", :d=>"d", :e=>"e", :bool=>false, :ords=>[], :keyrest=>{}}
parse.call %w[a -e e --bool]  # => {:a=>"a", :b=>"_", :d=>"_", :e=>"e", :bool=>true, :ords=>[], :keyrest=>{}}
parse.call %w[a -e e -x -y Y] # => {:a=>"a", :b=>"_", :d=>"_", :e=>"e", :bool=>false, :ords=>[], :keyrest=>{:x=>true, :y=>"Y"}}