how to declare a function accept an array of interface in golang?

Question

I want to declare a function accept array of interface, such as this:

func (this *CvStoreServiceImpl) setItemList(coll *mgo.Collection, itemList ...interface{}) (err error)

Howerver, when I call this function like as follow failed:

jobList := cvRaw.GetJobList()
this.setItemList(jobColl, jobList...)

here this the error:

cannot use cvRaw.GetJobList() (type []*cv_type.CvJobItemRaw) as type []interface {} in argument to this.setItemList

Go has no covariant types. You need to stuff your items in jobList into a []interface{} first before passing the []interface{} to your function. BTW. Don't use interface{}. — Volker
– Volker, Commented Nov 26, 2015 at 13:53
@Volker and what is difference between my code and this mgo insert method — roger
– roger, Commented Nov 26, 2015 at 13:57
Remove "..." 3 dots from "this.setItemList(jobColl, jobList...)", it should be this.setItemList(jobColl, jobList), jobList is already an array — Prashant Thakkar
– Prashant Thakkar, Commented Nov 26, 2015 at 14:23
@PrashantThakkar that is not right, jobList will become just one parameter, such as [3, 4, 5], if without ...., it becomes [[3, 4, 5]] — roger
– roger, Commented Nov 26, 2015 at 14:25

Mike Graf · Accepted Answer · 2016-02-26 00:45:34Z

2

I think what you're looking for is this

package main

import "fmt"

func main() {
    interfacetious := []interface{}{"s", 123, float64(999)}
    stuff(interfacetious)
    stuff2(interfacetious...)

    stuff2("or", 123, "separate", float64(99), "values")
}

// Stuff can only work with slice of things
func stuff(s []interface{}) {
    fmt.Println(s)
}

// Stuff2 is polyvaridc and can handle individual vars, or a slice with ...
func stuff2(s ...interface{}) {
    fmt.Println(s)
}

answered Feb 26, 2016 at 0:45

Mike Graf

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Comments

2 revs user13631587 · Accepted Answer · 2020-06-16 17:38:53Z

2

The question correctly declares the setItemList method, assuming that you want a variadic argument. Because the setList function works with any Mongo document type, it is appropriate to use interface{} in this scenario.

A []*cv_type.CvJobItemRaw cannot be converted to a []interface{}. Write a loop to create the []interface{} from jobList.

jobList := cvRaw.GetJobList()
s := make([]interface{}, len(t))
for i, v := range t {
    s[i] = v
}
this.setItemList(jobColl, s...)

See the Go Language FAQ for more details.

edited Jun 16, 2020 at 17:38

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