Go - constant variables and const keyword

Brief

Programming languages have the notion of constants which means “variables that can not be mutated once declared and initialized”.

Go also has almost the same meaning, but in a different context. To initialize a variable as a constant with a value of 10, we can do something like this:

const DISCOUNT = 10

In Go, constants mean “storing a literal to a variable”, this can be seen as a version of pattern matching in Erlang.

Literals in go are constructs that can create an instance of strings, numbers, booleans, composite structures, functions, or expressions. Hence unlike many programming languages, constants in go can be const FN = fun () { fmt.Println("Hello World") }.

An explanation

Initializing a variable as a constant means the variable holds the value and possibly the type of the literal it is assigned to. Anywhere the DISCOUNT above is used, the compiler assumes that as writing the integer literal 10.

At compile time, the compiler swaps all representations of a constant value with the value it was assigned to. Such that

func main () {
  fmt.Println("%v", DISCOUNT)
}

would become

func main () {
  fmt.Println("%v", 10)
}

Big difference

In some programming languages, Constants mean the value of a variable once declared and initialized can never change

In contrast to what we have understood – constants are used to enforce that a variable is immutable, in Go, constants can be used to assign names to a literal exactly once, while at compile time, the name is swapped with the value of the constant - ensuring cleaner code, the idiomatic go.

Shalom…