How to properly declare a map in Go?

A map can be declared in several ways:

1. Using var:

   // declaring a map without initialization
   // value is nil
   var myMap map[string]int
   

2. Using make:

   // declaring and initializing an empty map
   myMap := make(map[string]int)
   
   // declaring and initializing a map with a specified capacity
   // can improve performance with a large number of elements
   myMapWithCapacity := make(map[string]int, 100)
   

3. Using a literal:

   // declaring and initializing with initial values
   myMapWithValues := map[string]int{
       "key1": 1,
       "key2": 2,
   }
   
   // declaring and initializing an empty map
   // equivalent to make(map[string]int)
   emptyMapLiteral := map[string]int{}
   

Differences between methods:

Method	Default initialization	Capacity specification	Adding initial values
var	nil	No	No
make	Empty map	Yes	No
Literal {}	Empty map	No	Yes

It is important to remember that a map declared with var without initialization (nil) cannot be used to add or retrieve elements. Such operations will cause a panic. It must be initialized with make or a literal.