How to assign the first non-empty/nil value?

Question

This can be done in python / javascript:

# Python:
a = ""
b = "test"
c = a or b # test

// javascript
a = "";
b = "test";
c = a || b; // test

Can the same be accomplished in go without doing some conditional block? The only way I'm able to do this so far is with conditional blocks...

a := ""
b := "test"
var c
if a {
    c = a
} else {
    c = b
}

I think this is answer is going to be "no, this cannot be done", but I figured I would ask just in case I'm wrong. The example here is simplified. The variables a and b could have been defined long ago...

Answer 1

Go 1.22

If you want to assign the first non-zero value, starting with Go 1.22 you can use cmp.Or. It's basically like a "coalesce" operator in Javascript ?? or COALESCE() function in some database engines.

package main

import (
    "cmp"
    "fmt"
)

func main() {
    var a = ""
    var b = "test"

    c := cmp.Or(a, b)
    
    fmt.Println(c) // test
}

Obviously you can also assign to an existing variable; it comes in handy to simplify "if-nil-assign" idioms:

var a = ""
var b = "test"

a = cmp.Or(a, b)
// a is now "test"

The function is variadic, so it can take any number of arguments. The only catch is that it's also generic in T comparable, therefore after instantiation the varargs must have the same type. For more information about this detail, see Difference between any/interface{} as constraint vs. type of argument?

Answer 2

From golang FAQ, There is no ternary testing operation in Go. You may use the following to achieve the same result:

if expr {
    n = trueVal
} else {
    n = falseVal
}