晶体中的对象数组

Question

初学者问题：

如何用晶体中的结构制作一系列对象？还是如何在晶体中制作一系列对象？我正在尝试模仿GO代码。

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",
   },
}

更改为课程可以使我返回一个新对象。我敢肯定，在晶体中制作新对象的错误方法是错误的？然后，我可以在数组中添加对象。

  class Book 
    def initialize(id : Int32, title : String, author : String, desc : String)
      @id = id
      @title = title
      @author = author
      @desc = desc
    end

    def object 
      {
        @id,
        @title,
        @author,
        @desc
    }
    end 

  end


  books = [] of Book <--- HOW TO SET ARRAY OF OBJECTS ON THE TYPE?
  book1 = Book.new(1, "Hello", "Me", "This is a test.")
  puts book1.object
  books << book1.object
  puts books

Answer 1

您可以写作

books = [] of Book
books << book1

，也可以简单地执行此操作，然后让Crystal识别类型：

books = [book1]

最接近原件的是

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

编辑：如果您需要JSON，则需要实现它，例如 with-to-json“ rel =“ rel =“ nofollow noreferrer”>。最简单的是包括JSON :: serializable ：

require "json"

module TestBookJSON

  struct Book
    include JSON::Serializable      # <-- this

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

  books = [] of Book
  book1 = Book.new(1, "Hello", "Me", "This is a test.")
  books << book1
  puts books.to_json
  # => [{"Id":1,"Title":"Hello","Author":"Me","Desc":"This is a test."}]

end

Answer 2

似乎我想要的是，与Go中的结构版本不一样，是一系列哈希，这反过来是一系列对象，因为一切都是晶体中的对象？*。

  hash = [] of Hash(Int32, String) # Array of Hashes
  hash0 = {0 => "Jackson0"}
  hash1 = {1 => "Jackson1"}
  hash2 = {2 => "Jackson2"}
  hash3 = {3 => "Jackson3"}

  #Append the hashes to the array

  hash << hash0
  hash << hash1
  hash << hash2
  hash << hash3

OR

  (0..3).each do |i| 
    hash << {i => "Jackson#{i}"}
  end
  RESULT : [{0 => "Jackson0"}, {1 => "Jackson1"}, {2 => "Jackson2"}, {3 => "Jackson3"}]

  # Display them as JSON

  get "/" do
    hash.to_json
  end

RESULT : [{"0":"Jackson0"},{"1":"Jackson1"},{"2":"Jackson2"},{"3":"Jackson3"}]

Which in turn can be queried using hash[0][1] 

RESULT : {"1": "Jackson1"}