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Datatypes

Go lang data types:

  • Basic type: Numbers (integer variety, float variety, complex variety), strings, and booleans come under this category.
  • Aggregate type: Array and structs come under this category.
  • Reference type: Pointers, slices, maps, functions, and channels come under this category.
  • Interface type

Aggregate types

Arrays

Arrays can store multiple values of same datatype. Arrays must be declared by specifying type and size. Arrays are 0 indexed as in other languages.

var arrayName = [length]dataype{value1, value2}     // size is declared & initialized, cannot expand
var arrayName = [...]datatype{values,values}        // size is expandable, length is inferred
var arrayName = [length]datatype{}     // if size is declared and initliazied empty
var arrayName [length]datatype         // declared, not initialized

// can also use the short notation
arrayName := [<length>]datatype{values}

// initialize specific indices
arr1 := [5]int{1:10,2:40}   // sets 2nd element to 10 and 3rd element to 40 = [0 10 40 0 0]

Array elements can be accessed using their index number:

var prices = [10]int{10,30,40,80}

prices[2] = 100     //modify value

Strings

String functions

Contains

Reference types

Slices

Slice is an abstraction of an Array. It is more flexible and can grow as it is of variable length. It is also index based. You create a slice using var sliceName []string to create a slice of type String.

var sliceName []datatype
sliceName = append(sliceName, value)    // to add values

Maps

Maps are like dicts in Python. Maps are created using the syntax var mapName = make(map[key-datatype]value-datatype)

var userData = make(map[string]string)     //use make to create empty map

//populate values
userData["firstName"] = "adhitha"
userData["lastName"] = "karikalan"

Sometimes, you would like to create a list or slice of maps:

var userData = make(map[string][string])    //stores info about 1 user

// create a slice of maps. The 2nd parameter is the initial size of the slice
//slices grow dynamically. So the init size is just syntactical.
var allUsers = make([]map[string][string], 10)  //stores all users

Features of a map

  • Unlike dicts in Python, Maps can only store values that match the data type specified during declaration

Structs

Structs hold values of mixed or multiple data types. It is built on arrays and maps. Structs are actually a custom type. To create a struct:

type structName struct {    //use type keyword to create new struct type
    key1 <datatype>
    key2 <datatype>
    key3 <datatype>
}

for example you can define a User type as below:

type UserData struct {
    firstName string
    lastName string
    address string
    age uint
    previousAddresses []string  //slice
    flightsBooked []map[string]string   //slice of maps
    mvp bool
}

You can create an instance as shown below:

var phoenixUsers = make([]UserData, 0)  //use make to create a slice of UserData types

var u1 = UserData {
    firstName: "aditha",
    lastName: "karikalan",
    address: "chola kingdom",
    age: 40
}

phoenixUsers = append(phoenixUsers, u1)

// to query the struct var, use . notation
fmt.Println(u1.age)     // using . notation