I found its weird, why []string can not be converted to []interface{} ?
I think it should be possible, because:
but in the example below, it will be a compilation error
func f(args ...interface{}){ } s := []string{"ssd", "rtt"} f(s...) why the language can't finish the conversion automatically?
Because []string and []interface{} have different in-memory layouts. This is obvious when you realise that an interface{} variable needs to know the type of the value it contains.
For a []string slice, the backing array only needs to hold the individual strings. For the []interface{} slice, you've got both type information and the string values (well, pointers to the string values, since a string is larger than a single word of memory). So converting from one type to the other will involve copying the data.
It would be confusing for Go to automatically perform a conversion, since it would make it difficult to reason about code. For example, a function call f(s) could modify the strings in the slice s if it was declared to take a []string argument, but not if it was declared to take a []interface{} argument.
Slice is basically just a reference to the underlying array, start pointer, length and capacity. So if it would be possible, then consider the following:
sliceOfStrings := []string{"one", "two", "three"} // prints ONE TWO THREE for i := range sliceOfStrings { fmt.Println(strings.ToUpper(sliceOfStrings[i])) } // imagine this is possible var sliceOfInterface = []interface{}(sliceOfStrings) // since it's array of interface{} now - we can do anything // let's put integer into the first position sliceOfInterface[0] = 1 // sliceOfStrings still points to the same array, and now "one" is replaced by 1 fmt.Println(strings.ToUpper(sliceOfStrings[0])) // BANG! This issue exists in Java and C#. In practice it happens rarely, but still. Given that in Go there is no automatic type conversions like int32 -> int64 it makes sense that you are forced to create a []interface{} copy if you really want to send []string as []interface{}. This way there can be no surprise - you wrote it explicitly, you know what you're doing. And if function will modify []interface{} - it won't hurt original []string.
