go - golang: slice of struct != slice of interface it implements? -


i have interface model, implemented struct person.

to model instance, have following helper functions:

func newmodel(c string) model {     switch c {     case "person":         return newperson()     }     return nil }  func newperson() *person {     return &person{} }

the above approach allows me return typed person instance (can add new models later same approach).

when attempted similar returning slice of models, error. code:

func newmodels(c string) []model {     switch c {     case "person":         return newpersons()     }     return nil }  func newpersons() *[]person {     var models []person     return &models }

go complains with: cannot use newpersons() (type []person) type []model in return argument

my goal return slice of whatever model type requested (whether []person, []futuremodel, []terminator2000, w/e). missing, , how can implement such solution?

this similar question answered: https://stackoverflow.com/a/12990540/727643

the short answer correct. slice of structs not equal slice of interface struct implements.

a []person , []model have different memory layouts. because types slices of have different memory layouts. model interface value means in memory 2 words in size. 1 word type information, other data. person struct size depends on fields contains. in order convert []person []model, need loop on array , type conversion each element.

since conversion o(n) operation , result in new slice being created, go refuses implicitly. can explicitly following code.

models := make([]model, len(persons)) i, v := range persons {     models[i] = model(v) } return models

and dskinner pointed out, want slice of pointers , not pointer slice. pointer slice not needed.

*[]person        // pointer slice []*person        // slice of pointers

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