main.go

package main

import (
	"fmt"

	"example.org/int/typ"
)

func main() {
	for item := range items {
		if item.StringValue() != nil {
			fmt.Println("Found a string value:", *item.StringValue())
		}
	}
}

func items(push func(typ.Variant) bool) {
	push(typ.Int32(1))
	push(typ.String("hat"))
	push(typ.String("bat"))
	push(typ.Int32(3000))
}

variant.go

package typ

type Variant interface {
	StringValue() *string
	Int32Value() *int32
}

type variant struct {
	stringValue *string
	int32Value  *int32
}

func String(value string) Variant {
	return variant{stringValue: &value}
}

func Int32(value int32) Variant {
	return variant{int32Value: &value}
}

func (t variant) StringValue() *string {
	return t.stringValue
}

func (t variant) Int32Value() *int32 {
	return t.int32Value
}