You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mapiter.go
    path of file: ./repos/corteza/extra/server-discovery/vendor/github.com/lestrrat-go/iter/mapiter
    
    the code of the file until where you have to start completion: package mapiter

import (
	"context"
	"fmt"
	"reflect"
	"sync"
)

// Iterate creates an iterator from arbitrary map types. This is not
// the most efficient tool, but it's the quickest way to create an
// iterator for maps.
// Also, note that you cannot make any assumptions on the order of
// pairs being returned.
func Iterate(ctx context.Context, m interface{}) (Iterator, error) {
	mrv := reflect.ValueOf(m)

	if mrv.Kind() != reflect.Map {
		return nil, fmt.Errorf(`argument must be a map (%s)`, mrv.Type())
	}

	ch := make(chan *Pair)
	go func(ctx context.Context, ch chan *Pair, mrv reflect.Value) {
		defer cl
    
func AsMap(ctx context.Context, s interface{}, v interface{}) error {
	var iter Iterator
	switch reflect.ValueOf(s).Kind() {
	case reflect.Map:
		x, err := Iterate(ctx, s)
		if err != nil {
			return fmt.Errorf(`failed to iterate over map type: %w`, err)
		}
		iter = x
	default:
		ssrc, ok := s.(Source)
		if !ok {
			return fmt.Errorf(`cannot iterate over %T: not a mapiter.Source type`, s)
		}
		iter = ssrc.Iterate(ctx)
	}

	dst := reflect.ValueOf(v)

	// dst MUST be a pointer to a map type
	if kind := dst.Kind(); kind != reflect.Ptr {
		return fmt.Errorf(`dst must be a pointer to a map (%s)`, dst.Type())
	}

	dst = dst.Elem()
	if dst.Kind() != reflect.Map {
		return fmt.Errorf(`dst must be a pointer to a map (%s)`, dst.Type())
	}

	if dst.IsNil() {
		dst.Set(reflect.MakeMap(dst.Type()))
	}

	// dst must be assignable
	if !dst.CanSet() {
		return fmt.Errorf(`dst is not writeable`)
	}

	keytyp := dst.Type().Key()
	valtyp := dst.Type().Elem()

	for iter.Next(ctx) {
		pair := iter.Pair()

		rvkey := reflect.ValueOf(pair.Key)
		rvvalue := reflect.ValueOf(pair.Value)

		if !rvkey.Type().AssignableTo(keytyp) {
			return fmt.Errorf(`cannot assign key of type %s to map key of type %s`, rvkey.Type(), keytyp)
		}

		switch rvvalue.Kind() {
		// we can only check if we can assign to rvvalue to valtyp if it's non-nil
		case reflect.Invalid:
			rvvalue = reflect.New(valtyp).Elem()
		default:
			if !rvvalue.Type().AssignableTo(valtyp) {
				return fmt.Errorf(`cannot assign value of type %s to map value of type %s`, rvvalue.Type(), valtyp)
			}
		}

		dst.SetMapIndex(rvkey, rvvalue)
	}

	return nil
}