Golang - best practices to pass and return variables

Question

I am trying to create a web project with the julienschmidt/httprouter. I am searching to create a well formatted and well structured project so I have two questions about performances passing and returning value or pointers.
In my case I want to create a function that from the request returns an object so I have created it:

// StoreController
func (storeController *StoreController) New(w http.ResponseWriter, r *http.Request) {
    store, err := utilities.GetStoreFromRequest(r)
    // other stuff
    return
}

// Utilities package
func GetStoreFromRequest(r *http.Request) (*models.Store, error) {
    store := models.Store{}
    err := json.NewDecoder(r.Body).Decode(&store)
    // return a pointer is better than returning an object?
    return &store, err
}

Is it right or it is better to create a store object in the storeController and pass it to the function like:

// StoreController
func (storeController *StoreController) New(w http.ResponseWriter, r *http.Request) {
    store := models.Store{}
    err := utilities.GetStoreFromRequest(r, &store)
    // other stuff
    return
}

// Utilities package
func GetStoreFromRequest(r *http.Request, store *models.Store) error {
    err := json.NewDecoder(r.Body).Decode(store)
    return err
}

The other question is about the pointer, is too paranoid to pass and return always pointers instead of object and errors or not?

Possible duplicate of Why should constructor of Go return address?; and Pointers vs. values in parameters and return values. — icza
– icza, Commented Nov 26, 2016 at 21:08

AniSkywalker · Accepted Answer · 2016-11-27 04:07:33Z

2

It's usually redundant and better to eliminate pointless parameters. In fact, by having it as a parameter it's actually initialized to its nil value. Here are all valid ways to do this:

func GetStoreFromRequest(r *http.Request) (store *models.Store, err error) {
    err = json.NewDecoder(r.Body).Decode(store)
    return
}

func GetStoreFromRequest(r *http.Request, store *models.Store) error {
    err := json.NewDecoder(r.Body).Decode(store)
    return err
}

func GetStoreFromRequest(r *http.Request) (*models.Store, error) {
    var store models.Store // or store := models.Store{}
    err = json.NewDecoder(r.Body).Decode(&store)
    return &store, err
}

It's usually best practice to keep local variables local--imagine passing a parameter i to be used in a for loop. Doesn't make much sense, right? So for this situation, I'd recommend options 1 or 3 (which are essentially the same execution) and leave the local variable out of the function signature.

answered Nov 27, 2016 at 4:07

AniSkywalker

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1 Comment

AniSkywalker Over a year ago

If I misunderstood the question, basically, pointers are when you need to modify the underlying data and values are when you need the value.

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