var vs := in Go

Question

In the Go web server example here: http://golang.org/doc/effective_go.html#web_server

The following line of code works

var addr = flag.String(\"addr\         


        

Answer 1

The Go Programming Language Specification

Short variable declarations

A short variable declaration uses the syntax:

ShortVarDecl = IdentifierList ":=" ExpressionList .

Short variable declarations may appear only inside functions.

In your example, changing the variable declaration statement outside a function body

var addr = flag.String("addr", ":1718", "http service address")

to a short variable declaration statement outside a function body

addr := flag.String("addr", ":1718", "http service address")

fails with compiler error "non-declaration statement outside function body."