Example
// +build linux
package lib
var OnlyAccessibleInLinux int // Will only be compiled in Linux
Negate a platform by placing ! before it:
// +build !windows
package lib
var NotWindows int // Will be compiled in all platforms but not Windows
List of platforms can be specified by separating them with spaces
// +build linux darwin plan9
package lib
var SomeUnix int // Will be compiled in linux, darwin and plan9 but not on others
