How to call func everytime when we use var

Question

How I can rewrite the below code so that whenever I use the var CsvVersion every time it calls the func and gives me the latest value?

package main import ( "fmt" "os" ) var ( DefaultValMap = map[string]string{ "CSV_VERSION": "v1", } CsvVersion = GetEnvOrDefault("CSV_VERSION") ) func GetEnvOrDefault(env string) string { if val := os.Getenv(env); val != "" { return val } return DefaultValMap[env] } func main() { fmt.Println(CsvVersion) os.Setenv("CSV_VERSION", "v2") fmt.Println(CsvVersion) fmt.Println(os.Getenv("CSV_VERSION")) }

Actual output

$ go build 1.go && ./1 v1 v1 v2

The output should be like this

$ go build 1.go && ./1 v1 v2 v2

Unrelated but go build works best without filename arguments. — Volker
– Volker, Commented Aug 4, 2021 at 11:06

Jonathan Hall · Accepted Answer · 2021-08-04 10:18:33Z

There is no way to do this exact thing in Go. Go, very much by design, avoids "magic" things like this. Instead, don't use a variable, use a function:

func CsvVersion() string { return GetEnvOrDefault("CSV_VERSION") }

However note: It's not (generally) possible to change environment variables after a program starts (except within the program itself, which has very limited utility), so checking an env variable on every use is usually just wasted effort. Read more about that here.

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