Go is statically typed. It uses C-family syntax, but with some differences. To declare the type of a variable, C-family uses prefix:

int x;

However, readability is not very good as we can’t read from left to right. Scala use colon syntax with suffix:

x: Int

Go uses suffix by dropping the colon:

x int

Declaration and Assignment

The var statement declares a variable, or a list of variables. Note the type is at last.

var power int

By default, Go assigns a zero value to variables. Integers are assigned 0, booleans false, strings "" and so on. Initial value can also be assigned at declaration, one per variable:

var power int = 9000
var c, python, java = true, false, "no!"
var (
	ToBe   bool       = false
	MaxInt uint64     = 1<<64 - 1
	z      complex128 = cmplx.Sqrt(-5 + 12i)

Variable declarations may be “factored” into blocks, as with import statements.

If an initializer is present, the type can be omitted; the variable will take the type of the initializer.

A var statement can be at package or function level. Inside a function, the := short assignment statement can be used to declare a variable and assign initial value to it. The type in := statement is inferred.

Like imports, Go won’t let you have unused variables. Declared by unused variables will cause compile error.

Redeclaration and Reassignment

In a := declaration a variable v may appear even if it has already been declared, provided:

  • this declaration is in the same scope as the existing declaration of v (if v is already declared in an outer scope, the declaration will create a new variable),
  • the corresponding value in the initialization is assignable to v, and
  • there is at least one other variable in the declaration that is being declared anew.

A main usage is error handling: err variable can be redeclared many times by reassigning to it.


Constants are declared like variables, but with the const keyword.

const Pi = 3.14

Constants cannot be declared using the := syntax.

Numeric constants are high-precision values. An untyped constant takes the type needed by its context, so a numeric constant can be passed to functions as int or float64 without any explict conversion.