How to pass function that converts to interface{}

Question

I'm trying to write a function that would open a file, build an object out of each line using another function it receives as parameter and return a slice of these objects, similar to this:

func readFile(filename string, transform func(string) interface {}) (list []interface {}) {
    if rawBytes, err := ioutil.ReadFile(filename); err != nil {
        log.Fatal(err)
    } else {
        lines := strings.Split(string(rawBytes), "\n")
        for i := range lines {
             t := transform(lines[i])
             list = append(list, t)
        }
    }
    return list
}

I've tried to use it like this:

func transform(line string) (myObject *MyType) {
    fields := strings.Split(line, "\t")

    myObject.someField = fields[0]
    myObject.anotherField = fields[1]
    (...)
    return myObject
}

And somewhere else I've called the original method like this:

readFile("path/to/file.txt", transform)

This gives me an error: cannot use transform (type func(string) *MyType) as type func(string) interface {} in function argument

Is there a different way to approach this problem in Go?

EDIT: Here's a similar but very simplified example of what I tried to do: http://play.golang.org/p/jLAsYojkII

Well, you can change transform signature to func transform(s string) interface{}, but I don't think it's correct and acceptable answer. — Kavu
– Kavu, Commented Feb 27, 2014 at 18:21
@Kavu It might work. If what you're suggesting is this: play.golang.org/p/V2nDekb6f5 it seems to work — Vitor De Mario
– Vitor De Mario, Commented Feb 27, 2014 at 18:26
@Kavu I can confirm it works. I just needed to get the output of readFile and transform it into a slice of MyType values. It's enough for me, if you want to post it as an answer, I'll be glad to accept it! — Vitor De Mario
– Vitor De Mario, Commented Feb 27, 2014 at 18:44

Jonathan Hall · Accepted Answer · 2014-11-25 15:46:38Z

2

Just change your transform function signature to func transform(s string) interface{}, but I don't think it is the best solution.

edited Nov 25, 2014 at 15:46

Jonathan Hall

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answered Feb 27, 2014 at 19:03

Kavu

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1 Comment

Agis Over a year ago

You can combine this with a type switch.

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