Golang Preprocessor like C-style compile switch

Question

Does GO language have a preprocessor? When I looked up internet, there was few approaches which *.pgo convert to *.go. And, I wonder if it is doable in Go

#ifdef COMPILE_OPTION
  {compile this code ... }
#elif 
  {compile another code ...}

or, #undef in c

Answer 1

The closest way to achieve this is by using build constraints. Example:

main.go

package main

func main() {
    println("main()")
    conditionalFunction()
}

a.go

// +build COMPILE_OPTION

package main

func conditionalFunction() {
    println("conditionalFunction")
}

b.go

// +build !COMPILE_OPTION

package main

func conditionalFunction() {
}

Output:

% go build -o example ; ./example
main()

% go build -o example -tags COMPILE_OPTION ; ./example
main()
conditionalFunction