如何在Golang中创建作为参数指定类型的切片？ 或如何为Appengine数据存储区getAll提供[]接口{}

Question

I'm trying to create a generator of handlers that works for several kinds of entities. The following code works if the items slice is of a specific type (eg: var items []Person), but I'm having problems generalizing it: specifically "ERROR: Can't get items: datastore: invalid entity type". Any idea of how to declare items so that it have a type valid for GetAll?

func ScaffoldList(entity interface{}, collection string, templ *template.Template) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request){
        c := appengine.NewContext(r)
        T := reflect.TypeOf(entity)
        q := datastore.NewQuery(T.String())
        items := reflect.MakeSlice(reflect.SliceOf(T), 0, 10)
        _, err := q.GetAll(c, &items)
        if err != nil{
            c.Errorf("Can't get items: %v", err)
            http.Error(w, "Can't get items", http.StatusInternalServerError)
            return
        }
        context.Set(r, collection, items)
        ion.RenderTemplate(templ).ServeHTTP(w, r)
    })
}

Answer 1

Here's how you get an argument of type *[]Person:

items := reflect.New(reflect.SliceOf(T))
_, err := q.GetAll(c, items.Interface())

GetAll will allocate the backing array for the slice. There's no need to preallocate the backing array with make.

Assuming that the argument to context.Set is a value containing a slice, then you need to dereference the pointer:

context.Set(r, collection, items.Elem())

If the context does not work with reflect values, then you probably want:

context.Set(r, collection, items.Elem().Interface())