GoLang Structs

In Golang, structs are simple containers for data.

• can have fields
• no methods attached to them
  • methods defined separately and associated with a struct type.

The following show a simple Book class equivalents in Ruby and GoLang.

class Book
  attr_reader(:title, :author)

  def initalize(title, author)
    @title  = title
    @author = authoer
  end
end

# usage
book = Book.new('Title', 'Jon Snow')

// Equivalent to `class Book` in ruby
type Book struct {
  Title string,
  Author string
}

Instantiating GoLang type

Composite Literal

Composite Literal is syntax to create an initialise composite types in one step. We can instantiate the following types:

• structs
• arrays
• slices
• maps

Here we are assigning a new Book instance to the variable book

// Composite Literal
book := Book{
  Title: "Title",
  Author: "Author"
}

Using new keyword

The longer form is to use the new keyword. This would be similar to the way we would instantiate a class in Ruby with book = Book.new(..)

We would assign the attributes of the book (i.e. Title and Author) using = sign.

// Using the `new` keyword
book        := new(Book)
book.Title  = "Book Title"
book.Author = "John Snow"

Without Short Variable Declaration (:=)

Notice that we used the symbol := in the first example?

It's syntactic sugar for the following verbose way of declaring a variable and assigning it a value.

// Without Short Virable Declaration

// Example 1
var book Book // Declare variable `book` of type `Book`
book.Title = "Book Title" // Assign the value to book variable
book.Author = "John Snow"

// Example 2
var count int
count = 20

Factory Function

We could also use the factory pattern to make it easier when initialising the struct when we need to:

• add additional logic
• add default values

Assuming we would want to make each first character of the book's title and author tokens to be capitalised.

// Factory Function
func NewBook(title string, author string) Book {
  return Book{
    Title: titlelise(title), // default logic to "titlelise" 
    Author: titlelist(author)
  }
}

func titlelise(str string) {
  caser := cases.Title(lanaguage.English)
  return caser.String(str)
}

Attaching a function to a struct

In Ruby, we would simply define a function within the class. Here, we are defining a function called to_string() to print the book title name author.

class Book
  attr_reader(:title, :author)

  def initalize(title, author)
    @title  = title
    @author = authoer
  end

  # new function we added
  def to_string()
    put "#{title} by #{string}"
  end
end

In GoLang, we would "attach" the function by passing in the stuct to the function.

// Equivalent to `class Book` in ruby
type Book struct {
  Title string,
  Author string
}

// Attaching the function to the `struct`
func (book Book) ToString() string {
  return fmt.Sprintf("%s by %s", book.Title, book.Author)
}

// Usage
book := Book{
  Title: "Title",
  Author: "Author"
}

book.ToString()
// => Title by Author

Explanation of:

func (book Book) ToString() string

Token

Description

func

function keyword

(book Book)

Attaching the function to the type Book struct

Token	Description
func	function keyword
(book Book)	Attaching the function to the type Book struct - book: variable to access the struct within the function - Book: type of the struct
ToString()	name of the function
string	return type of the function

- book: variable to access the struct within the function- Book: type of the struct

ToString()

name of the function

string

return type of the function

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