Data Types

Data types are the classifications given to the different kinds of values used in everyday programming. In Go, there are seven fundamental data types: Numbers, Strings, Booleans, Arrays, Structs, Slices, and Pointers.

Numbers

In Go, any number is regarded as number, but there are three sub-categories:

• Integers (signed and unsigned)
• Floating-point numbers
• Complex numbers

Integers

Integers are number-types that are either:

• Signed (int) integers that can be positive or negative.
• Unsigned (uint) integers ranging from 0 to positive infinity.

Each integer value comes in 4 different memory sizes.

• 8-bit: int8/uint8
• 16-bit: int16/uint16
• 32-bit: int32/uint32
• 64-bit: int64/uint64
• 32- or 64-bit based on system architecture: int/uint
• Synonym for int32: rune
• synonym for int8: byte

Floating-Point Numbers

Floating-point numbers can contain a decimal point. There are two different sizes.

• 32-bit: float32
• 64-bit: float64

Complex Numbers

Complex numbers are composed of a real number and an imaginary number. The real number is either a float. There are two different sizes:

• 32-bit float + imaginary number: complex64
• 64-bit float + imaginary number: complex128

// Initialize with complex() taking 2 arguments: a float and a complex number
var complex complex64 = complex(1, 2) // Equals 1 + 2i

Variables can also be initialized with a shorthand:

complex := 1 + 2i

Strings

A string represents a sequence of characters. Strings are immutable; once they are created they can’t be modified.

var s string

s = "Hello, World!"

Booleans

A boolean can hold one of two possible values, either true or false.

var isValid bool

isValid = true
isValid = false

Arrays

Arrays are list with static capacity. They can’t change their capacity after the declaration.

// Declare and initialize an array of capacity 5 and fill it with elements
someArray := [5]int{0, 2, 3, 4, 5}

Slices

Slices can change their capacity dynamically even after their declaration. Under the hood a slice references an array. If the array changes, so does the slice.

// Copy the elements from index 0 until (excluding) index 3 into a slice
var slice []int = someArary[0:3]

Structs

In Go, a struct is a more complex type that can contain custom fields. It’s similar to an object in JavaScript or a dictionary in Python. The fields of a struct can be accessed with a dot ..

// Declaration with "type ... struct" keywords
type Box struct {
  X int
  Y int
 }

Structs are initialized by:

1. Referencing the name of the struct
2. Passing zero, any or all of the fields of the struct.

The fields without a value will be initialized with zero-values by default.

// Initialization
b := Box{1, 2}

Pointers

Pointers contain the memory address of the variable they are based on. Pointers used *.

// Declaration of a pointer with *
var p *int

someInteger := 42

// Create pointer from variable using "&"
p = &someInteger