Loop over array of items that implement an interface

Question

Suppose I have an array of items that implement an interface Reader:

var items []Foo

How would I pass these items into a function that takes readers?

func (items []Reader) { ... }

I can't use the type []Reader because I get an error like:

Cannot use type `[]Foo` as type `[]Reader`...

See golang.org/doc/faq#convert_slice_of_interface (and substitute io.Reader for interface{} when reading). — Dave C
– Dave C, Commented Mar 31, 2015 at 20:17

peterSO · Accepted Answer · 2015-03-31 20:40:20Z

2

For example,

package main

import (
    "bytes"
    "io"
)

var items []*bytes.Buffer

func f(items []io.Reader) {}

func main() {
    readers := make([]io.Reader, len(items))
    for i, item := range items {
        readers[i] = item
    }
    f(readers)
}

answered Mar 31, 2015 at 20:40

peterSO

168k32 gold badges303 silver badges293 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Vlad the Impala Over a year ago

That works, but it means I have to loop over all the items before I call the function. I was trying to avoid the loop.

peterSO Over a year ago

@VladtheImpala: Because they do not have the same representation in memory, it is necessary to copy the elements individually. Can I convert a []T to an []interface{}?

Jerry Saravia · Accepted Answer · 2015-04-02 03:42:12Z

1

Similar to peterSO's answer.

package main

import (
    "bytes"
    "io"
)

type Foo struct{}
type Foos []Foo


func (f Foos) toReaders() []io.Reader {
    readers := make([]io.Reader, len(f))
    for i, item := range f {
        readers[i] = item
    }
    return  readers
}

func f(items []io.Reader) {}

func main() {
    var x Foos
    f(x.toReaders())
}

answered Apr 2, 2015 at 3:42

Jerry Saravia

3,8573 gold badges26 silver badges40 bronze badges

Collectives™ on Stack Overflow

Loop over array of items that implement an interface

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related