Named Parameters in Ruby Structs

Question

I\'m pretty new to Ruby so apologies if this is an obvious question.

I\'d like to use named parameters when instantiating a Struct, i.e. be able to specify which ite

Answer 1

Ruby 2.x only (2.1 if you want required keyword args). Only tested in MRI.

def Struct.new_with_kwargs(lamb)
  members = lamb.parameters.map(&:last)
  Struct.new(*members) do
    define_method(:initialize) do |*args|
      super(* lamb.(*args))
    end
  end
end

Foo = Struct.new_with_kwargs(
  ->(a, b=1, *splat, c:, d: 2, **kwargs) do
    # must return an array with values in the same order as lambda args
    [a, b, splat, c, d, kwargs]
  end
)

Usage:

> Foo.new(-1, 3, 4, c: 5, other: 'foo')
=> #"foo"}>

The minor downside is that you have to ensure the lambda returns the values in the correct order; the big upside is that you have the full power of ruby 2's keyword args.