golang变量替换

Question

How can I use variable substitution in go?

For example, I have the following code:

debug_level := "Info"
log.Info("Debug Test")

Can I use a variable debug_level for the log function instead of passing a direct argument? Something like:

debug_level := "Info"
log.${debug_level}("Debug Test")

Thank you.

Answer 1

Go is a statically typed language, if you would call a function or method by name, the compiler could not check if the parameters you provide match the signature of the function.

Instead use function variables: your variable that currently holds the method or function name can be be a variable of function type, holding a function or method value.

Let's assume we have the following logging functions:

func Info(args ...interface{}) {
    fmt.Print("[Info] ")
    fmt.Println(args...)
}

func Error(args ...interface{}) {
    fmt.Print("[Error] ")
    fmt.Println(args...)
}

You may use it like this:

var logger func(...interface{}) = Info

func main() {
    logger("something")
    logger = Error
    logger("Some other thing")
}

Output will be (try it on the Go Playground):

[Info] something
[Error] Some other thing

Also note that this works with methods too, not just with functions:

type Logger struct{}

func (l Logger) Info(args ...interface{}) {
    fmt.Print("[Info] ")
    fmt.Println(args...)
}

func (l Logger) Error(args ...interface{}) {
    fmt.Print("[Error] ")
    fmt.Println(args...)
}

Using it:

var mainLogger = Logger{}

var logger func(...interface{}) = mainLogger.Info

func main() {
    logger("something")
    logger = mainLogger.Error
    logger("Some other thing")
}

Output (try it on the Go Playground):

[Info] something
[Error] Some other thing

See related question: golang function alias on method receiver