Go structs

Go structs

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A struct is a data type that groups together values of different types. Structs are useful for organizing related data into a single entity, hence making it easy to work with. This is a great use of abstracting away data.

To define a struct, you use the type keyword followed by the name of the struct, the struct keyword and finally, the list of fields enclosed within curly braces (This method of using type, name and then the variable type is go's way of defining custom data types). Each field has a name and a type. For example, the following code defines a person struct with two fields:

type person struct {
  name string
  age int
}

There are multiple ways of creating a variable of a particular struct type. To make one of the person type, you can use the following ways:

By using the struct literal.

p1 := person{                   // p1 = person{"Rajiv", 30}
  name: "Rajiv",
  age: 30,
}

// Adding an '&' creates a pointer of type person
p2 := &person{                  // p2 = &person{"Rajiv", 30}
  name: "Rajiv",
  age: 30,
}

// Make sure to pass the values in the correct order
// This avoids having to add the field name 
p3 := person{"Rajiv", 30}      // p3 = person{"Rajiv", 30}

Without using the struct literal, via the new keyword.

This returns a pointer to the created struct.

p := new(person)
p.name = "Rajiv"
p.age = 30                      // p = &person{"Rajiv", 30}

Once you have created a struct value, you can access its fields using the dot notation. For example, the following code accesses the name field of the person struct p:

fmt.Println(p.Name)  // "Rajiv"

Along with accessing fields, you can also modify the values of fields using the dot notation. For example, the following code sets the age field of the person struct p to 35:

p.Age = 35
fmt.Println(p.Age) // 35

One of the key advantages of using structs in Go is that they allow you to define custom data types that can be used throughout your program. This makes it easier to write modular and reusable code, as you can define a struct that encapsulates a particular set of data and then use that struct wherever you need to work with that data.

For example, the following code defines a book struct with fields for the book's title, author, and page count:

type book struct {
  title string
  author string
  pages int
}

This book struct can be used to represent a book in your program. You can create a book struct value by providing values for each of the fields, as in the following example:

bk := book{
  title: "Oliver Twist",
  author: "Charles Dickens",
  pages: 373,
}

Once you have created a book struct, you can access and manipulate its fields using the dot notation, as in the previous example. For instance, the following code prints the title and author of the book struct bk:

fmt.Printf("%s by %s\n", bk.Title, bk.Author)  // Oliver Twist by Charles Dickens

Sidenote: Using lowercase letters to name a field (eg: title field in the book struct) makes it such that it can't be used outside the package the struct was defined in. This is similar to how methods and functions in go can't be used outside the package if they start with a lowercase letter.

Methods

In addition to defining custom data types, structs also allow you to define methods that operate on the struct's data. A method is a function that is associated with a struct and has access to the struct's fields. This allows you to define behaviour that is specific to your struct and that can be easily invoked on any variable of the particular struct value.

For example, the following code defines a book struct with a PrintInfo method that prints the book's title, author, and page count:

type book struct {
  title string
  author string
  pages int
}

func (b *book) PrintInfo() {
  fmt.Printf("%s by %s (%d pages)\n", b.Title, b.Author, b.Pages)
}

Here, the PrintInfo method is defined as a function that takes a pointer to the book struct (*book) as its receiver. This means that the PrintInfo method can be called on any variable of the type book struct using the dot notation as in the following example:

bk := &book{"Oliver Twist", "Charles Dickens", 373}
bk.PrintInfo()  // Oliver Twist by Charles Dickens (373 pages)

In this example, the PrintInfo method is called on the book struct bk, and it prints the title, author, and page count of the book. This allows you to easily print out information about the book without having to manually construct the output string.

Well, I hope this blog gave you a fair overview of structs in go and I hope you liked it.