Variable declarations

August 11, 2023

I don’t know about you, but I feel like we’ve just spent a month trudging through a dense jungle of generics details… let’s talk about something a bit more applicable to all of our code:

Variable declarations

A variable declaration creates one or more, binds corresponding identifiers to them, and gives each a type and an initial value.

VarDecl     = "var" ( VarSpec | "(" { VarSpec ";" } ")" ) .
VarSpec     = IdentifierList ( Type [ "=" ExpressionList ] | "=" ExpressionList ) .

Now we’re back in some more familiar territory!

Virtually every language has some form of variable declaration, so this should very familiar to you, even if you’ve never written a line of Go code in your life.

We’re presented with a number of examples to make it all more clear:

var i int
var U, V, W float64
var k = 0
var x, y float32 = -1, -2
var (
	i       int
	u, v, s = 2.0, 3.0, "bar"
var re, im = complexSqrt(-1)
var _, found = entries[name]  // map lookup; only interested in "found"

If a list of expressions is given, the variables are initialized with the expressions following the rules for assignment statements. Otherwise, each variable is initialized to its zero value.

This last point is where Go differs from some other languages. You can never have an “uninitialized” variable in Go. Every variable is initialized either to a value you specify, as in:

var x = 3

Or to the zero value for its type:

var x int // x == 0

Quotes from The Go Programming Language Specification Version of August 2, 2023

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