I know that I can use compiler flag in Go for variables, but how to do it for constants?
I would like to set some constants, like database sets, at compile time like that:
package db_info
var Deploy string
const DbType = "mysql"
const DbUser = "my_user"
const Db = "my_db"
const DbPort = "3306"
if Deploy == "staging" {
const DbPassword = "my_pwd_stg"
const DbHost = "db.url.com"
} else if Deploy == "production" {
const DbPassword = "my_pwd_prd"
const DbHost = "db.url.com"
} else {
const DbPassword = "pwd"
const DbHost = "127.0.0.1"
}
How to do it in correctly? Like that I got:
syntax error: non-declaration statement outside function body
You cannot do that. It would break the scoping rules. You would expect the constants to be globally visible but they are defined within a block.
I would just pass those values as program parameters or environment variables.
On the other hand, as you mentioned, you can modify string variables at the compilation time. Use -ldflags to do it.
go run -ldflags="-X main.who=Something" hello.go
in
package main
import "fmt"
var who = "World"
func main() {
fmt.Printf("Hello, %s.
", who)
}
See https://blog.cloudflare.com/setting-go-variables-at-compile-time/