表示功能，可任意分割

Question

I want to express a function that can take any slice. I thought that I could do this:

func myFunc(list []interface{}) {
  for _, i := range list {
    ...
    some_other_fun(i)
    ...
  }
}

where some_other_fun(..) itself takes an interface{} type. However, this doesn't work because you can't pass []DEFINITE_TYPE as []interface{}. See: https://golang.org/doc/faq#convert_slice_of_interface which notes that the representation of an []interface{} is different. This answer sums up why but with respect to pointers to interfaces instead of slices of interfaces, but the reason is the same: Why can't I assign a *Struct to an *Interface?.

The suggestion provided at the golang.org link above suggests rebuilding a new interface slice from the DEFINITE_TYPE slice. However, this is not practical to do everywhere in the code that I want to call this function (This function is itself meant to abbreviate only 9 lines of code, but those 9 lines appear quite frequently in our code).

In every case that I want to invoke the function I would be passing a []*DEFINITE_TYPE which I at first thought would be easier to abstract until, again, I discovered Why can't I assign a *Struct to an *Interface? (also linked above).

Further, everytime I want to invoke the function it is with a different DEFINITE_TYPE so implementing n examples for the n types would not save me any lines of code or make my code any clearer (quite the contrary!).

It is frustrating that I can't do this since the 9 lines are idiomatic in our code and a mistype could easily introduce a bug. I'm really missing generics. Is there really no way to do this?!!

Answer 1

Probably the best thing to do is to define an interface that encapsulates what myFunc needs to do with the slice (i.e., in your example, get the nth element). Then the argument to the function is that interface type and you define the interface method(s) for each type you want to pass to the function.

You can also do it with the reflect package, but that's probably not a great idea since it will panic if you pass something other than a slice (or array or string).

func myFunc(list interface{}) {
    listVal := reflect.ValueOf(list)
    for i := 0; i < listVal.Len(); i++ {
        //...
        some_other_fun(listVal.Index(i).Interface())
        //...
    }
}

See https://play.golang.org/p/TyzT3lBEjB.