Conditional compilation in Go

We often want to change method behavior in each environment such as production or staging.

Go supports conditional compilation with build tool options.

Build Constraints

build - The Go Programming Language

As an example, There are these files in a repository.

debug.go

// +build debug
package main
import (
    "log"
    "time"
)
func Now() {
    log.Print("debug mode")
    log.Print(time.Now())
}

release.go

// +build !debug
package main
import (
    "log"
    "time"
)
func Now() {
    log.Print(time.Now())
}

main.go

package main
func main() {
    Now()
}

Go has -tags build options. This option reacts to the magic comment // +buildwhich are the top of source files.

When building source files, we can specify tags of which file to build.

$ go build
$ ./app
2018/05/09 21:51:51 2018-05-09 21:51:51.418615533 +0900 JST m=+0.000285531
$ go build -tags debug
$ ./app
2018/05/09 21:51:51 debug mode
2018/05/09 21:51:51 2018-05-09 21:51:51.418615533 +0900 JST m=+0.000285531

By using -tags build options, We can switch any values or method behavior in each environment.