Converting a pulumi.IDOutput to a string and using it in a lookup function

main.go

package main

import (
	"fmt"

	"github.com/pulumi/pulumi-aws/sdk/v5/go/aws/ec2"
	"github.com/pulumi/pulumi/sdk/v3/go/pulumi"
)

func main() {
	pulumi.Run(func(ctx *pulumi.Context) error {

		vpc, err := ec2.NewVpc(ctx, "vpc", &ec2.VpcArgs{
			CidrBlock:          pulumi.String("10.0.0.0/16"),
			EnableDnsHostnames: pulumi.Bool(true),
			EnableDnsSupport:   pulumi.Bool(true),
		})
		if err != nil {
			return err
		}

		// Convert the ID to an output of string.
		vpcID := vpc.ID().ToStringOutput()

		// Use the string output to look up the associated route table.
		// NOTE:
		//       We will not be able to create a variable outside, assign inside
		//         and use it later.
		//       This is the case because `Apply` does **not** block!
		//       We will always end up with an empty or nil value!
		_ = vpcID.ApplyT(func(id string) string {
			routeTableResult, err := ec2.LookupRouteTable(ctx, &ec2.LookupRouteTableArgs{
				VpcId: &id,
				Filters: []ec2.GetRouteTableFilter{
					{
						Name:   "vpc-id",
						Values: []string{id},
					},
					{
						Name:   "association.main",
						Values: []string{"true"},
					},
				},
			})
			if err != nil {
				return ""
			}
			
			// Log the looked-up route table ID.
			fmt.Printf("%s", routeTableResult.RouteTableId)

			return id
		}).(pulumi.StringOutput)

		return nil
	})
}