Pass an interface{} type with pointer value to an interface{} parameter

Question

I have two function in my code, a parent function with interface{} parameter type and another child function with interface{} parameter type. I called childFunc in parentFunc and assert parent param to *interface{} and pass it to childFunc and at the end i called parent function with &user argument

func childFunc(param interface{}){}

func parentFunc(param interface{}){
     childFunc(*(param.(*interface{})))
}

parentFunc(&user)

but i have this error:

interface conversion: interface {} is *models.User, not *interface {}

what is the problem? how can i solve this problem?

this is my real code.

func Update(context echo.Context, modelUpdatedInstance interface{}, constraints map[string]interface{}) error {

    /* Validation */
    //test := modelUpdatedInstance.(*interface{})
    _, validationErrors := govalidator.ValidateStruct(*(modelUpdatedInstance.(*interface{})))
    if validationErrors != nil {
        return validation.CheckValidation(context, validationErrors)
    }

    if constraints != nil {
        database.DB.First(modelUpdatedInstance, constraints["id"]).Model(modelUpdatedInstance).Updates(modelUpdatedInstance)
    } else {
        return context.JSON(http.StatusBadRequest, map[string]interface{}{"Errors": []string{"no identifier"}})
    }

    return context.JSON(http.StatusOK, *(modelUpdatedInstance.(*interface{})))
}

The error tells you exactly what is wrong. Your value is of type `*models.User`, not `*interface{}`, so trying to convert it to `*interface{}` fails. What is your question? — Jonathan Hall, Jul 26 '20 at 14:55
my child function only works on value only not reference, i intend to pass value of reference to child function. thanx for quick reply — Bahman Binary, Jul 26 '20 at 15:04
Go always, only passes by value--there is no pass by reference in Go at all. So it seems you're trying to solve a problem that cannot exist. — Jonathan Hall, Jul 26 '20 at 15:05
You cannot pass by reference in Go. See here: https://stackoverflow.com/q/47296325/13860 — Jonathan Hall, Jul 26 '20 at 15:12
@Flimzy i read that post, my problem is that i want to pass value of `user` to child function not `&user`(not pointer) — Bahman Binary, Jul 26 '20 at 15:22
@MuffinTop for passing `user` value to child function i should assert it and when assert it, it cause error — Bahman Binary, Jul 26 '20 at 15:25
@MuffinTop i insert code to question i want to insert value of `modelUpdatedInstance` in `ValidateStruct` — Bahman Binary, Jul 26 '20 at 15:34
@BahmanBinary: So what's stopping you from using only a user value, and not a pointer value? — Jonathan Hall, Jul 26 '20 at 15:59

Charlie Tumahai · Answer 1 · 2020-07-26T17:30:15.487

0

The govalidator.ValidateStruct function expects a pointer to a struct. The top caller has a pointer to a struct.

Simply pass the pointer through the calls.

func top() {
    childFunc(&user{})
}

func parentFunc(param interface{}) {
    childFunc(param)
}

func childFunc(param interface{}) {
    _, err := govalidator.ValidateStruct(param)
    ...
}

Run it on the playground.

edited Jul 26 '20 at 17:30

answered Jul 26 '20 at 17:18

Charlie Tumahai

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i mean the question in this page: https://stackoverflow.com/questions/49540367/how-do-i-dereference-a-pointer-value-passed-as-the-empty-interface sorry for misleading you – Bahman Binary Jul 26 '20 at 19:48
is there any solution for that other than `reflect` – Bahman Binary Jul 26 '20 at 19:51
@BahmanBinary It's unclear how `reflect` or the linked question relates to the question. It looks like you are attempting to dereference pointers where you should use the pointer value. Remove the attempts to dereference the pointers from the code (including the type assertion) and try that. Report back with what does not work. – Charlie Tumahai Jul 26 '20 at 20:10

Pass an interface{} type with pointer value to an interface{} parameter

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