ActionController::Parameters

permit + require: every filtered key must be present and non-empty. expect({"post" => [:title, :body]}) — same Hash-argument style as permit.

permit(:title, {"author" => [:name]}) — nested/array filters are passed as a Hash argument instead of Ruby keyword syntax (documented deviation: Crystal can't take heterogeneous keyword splats here).

require(:post) returns the nested parameters themselves (as in Rails); require([:a, :b]) returns a Parameters holding those keys.

Appends a short String representation of this object which includes its class name and its object address.

class Person
  def initialize(@name : String, @age : Int32)
  end
end

Person.new("John", 32).to_s # => #<Person:0x10a199f20>