I have some server code that sends a request to an endpoint and receives a JSON response which is stored in an object that is of type empty interface. I have to parse out the information and store it in a slice of "Resource" objects, with Resource being an interface. The JSON data in my case represents a "Position" object, which satisfies the Resource interface. So basically the code for these look like this:
// Resource interface type
type Resource interface {
// Identifier returns the id for the object
Identifier() bson.ObjectId
// Description give a short description of the object
Description() string
// Initialize should configure a resource with defaults
Initialize()
// Collection name for resource
Collection() string
// Indexes for the resources
Indexes() []mgo.Index
// UserACL returns the user access control list
UserACL() *UserACL
// IsEqual should compare and return if resources are equal
IsEqual(other Resource) bool
// Refresh should update a resource from the database
Refresh()
}
And the position model is:
// Position model
type Position struct {
ID bson.ObjectId `json:"id" bson:"_id,omitempty" fake:"bson_id"`
Title string `json:"title" bson:"title" fake:"job_title"`
Summary string `json:"summary" bson:"summary,omitempty" fake:"paragraph"`
IsCurrent bool `json:"isCurrent" bson:"is_current,omitempty" fake:"bool"`
CompanyID bson.ObjectId `json:"company" bson:"company_id,omitempty" fake:"bson_id"`
UACL *UserACL `bson:"user_acl,omitempty" fake:"user_acl"`
}
// Identifier returns the id for the object
func (p *Position) Identifier() bson.ObjectId {
return p.ID
}
// Description give a short description of the object
func (p *Position) Description() string {
return fmt.Sprintf("[%v:%v]", p.Collection(), p.ID)
}
....(the other methods follow)
My endpoint is designed to retrieve a list of positions in my database, so this obviously means that the empty interface containing the JSON data contains a slice of Resources, and can't be type asserted into a slice (Go doesn't allow this) and instead done manually by iteration. So I followed through the code and isolated my problem to this:
func InterfaceSlice(slice interface{}) []Resource {
s := reflect.ValueOf(slice).Elem()
if s.Kind() != reflect.Slice {
panic("InterfaceSlice() given a non-slice type")
}
ret := make([]Resource, s.Len())
for i := 0; i < s.Len(); i++ {
r := s.Index(i)
rInterface := r.Interface()
ret[i] = rInterface.(Resource)
}
return ret
}
Everything in the above code is working just fine until
ret[i] = rInterface.(Resource)
and then my server blows up and panics. I looked through the Go documentation and as far as I can tell I should be able to type assert into Resource even though rInterface is an empty interface with Position model data because the Position type satisfies the Resource interface anyway. Am I correct in understanding this? Or is there something I'm missing?