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

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