proposal: make variadic function take arguments in a more flexible way

[stephane-archer]

In the following code:

func Greeting(prefix string, who ...string) {
}

// classic parameter passing
Greeting("nobody")
Greeting("hello:", "Joe", "Anna", "Eileen")

s := []string{"James", "Jasmine"}
// ... parameter passing
Greeting("goodbye:", s...)

Greeting("goodbye:", append([]string{"Kevin"},s...)...) // work but is not really convenient 
Greeting("goodbye:", "Kevin", s...) // is not working but would be nice

basically the ... operator can represent an "unpacking operation" and the compiler can see that Greeting("goodbye:", "Kevin", s...) doesn't break the prefix string, who ...string signature.

I hope this is clear
I think this would not break backcompatibily and make things nicer when working with variadic function

[seankhliao]

Duplicate of #18605