Meaning of …interface{} (dot dot dot interface)

A parameter type prefixed with three dots (…) is called a variadic parameter. That means you can pass any number or arguments into that parameter (just like with fmt.Printf()). The function will receive the list of arguments for the parameter as a slice of the type declared for the parameter ([]interface{} in your case). The Go Specification states:

The final parameter in a function signature may have a type prefixed with …. A function with such a parameter is called variadic and may be invoked with zero or more arguments for that parameter.

A parameter:

a ...interface{}

Is, for the function equivalent to:

a []interface{}

The difference is how you pass the arguments to such a function. It is done either by giving each element of the slice separately, or as a single slice, in which case you will have to suffix the slice-value with the three dots. The following examples will result in the same call:

fmt.Println("First", "Second", "Third")

Will do the same as:

s := []interface{}{"First", "Second", "Third"}

This is explained quite well in the Go Specification as well:

Given the function and calls

   func Greeting(prefix string, who ...string)
   Greeting("hello:", "Joe", "Anna", "Eileen")

within Greeting, who will have the value nil in the first call, and []string{"Joe", "Anna", "Eileen"} in the second.

If the final argument is assignable to a slice type []T, it may be passed unchanged as the value for a ...T parameter if the argument is followed by .... In this case no new slice is created.

Given the slice s and call

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

within Greeting, who will have the same value as s with the same underlying array.

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