Array of objects in Crystal

Beginner question:

How to make an Array of objects from a Struct in Crystal? Or how to make an array of objects in Crystal? I am trying to emulate the go code.

struct Book 
   def initialize(
     @Id : Int32,
     @Title : String,
     @Author : String, 
     @Desc : String
   )
   end
 end

 books = [] of Int32 | String <--- This is wrong
 book1 = Book.new(1, "Hello", "Me", "This is a test.")


GO CODE: 

type Book struct {
   Id     int    `json:"id"`
   Title  string `json:"title"`
   Author string `json:"author"`
   Desc   string `json:"desc"`
}

var Books = []models.Book{
   {
       Id:     1,
       Title:  "Golang",
       Author: "Gopher",
       Desc:   "A book for Go",
   },
}

>Solution :

You can write

books = [] of Book
books << book1

or you can simply do this, and let Crystal recognise the type:

books = [book1]

The closest to the original is

books = [
  Book.new(1, "Hello", "Me", "This is a test.")
]