Day 2 — Variables, Types & Zero Values

Learning Objectives

• Understand Go's static type system and why it prevents bugs
• Use const with iota for typed enumerations
• Know what zero values are and why they matter for network buffers

Key Concepts

// var declaration (explicit type)
var name string = "proxy"
var port int = 8080

// Short declaration (inferred type, only inside functions)
host := "localhost"
timeout := 30 * time.Second

// Constants — evaluated at compile time
const maxConnections = 10_000

// iota — auto-incrementing constant generator
type Protocol int

const (
    TCP  Protocol = iota // 0
    UDP                  // 1
    TLS                  // 2
    HTTP                 // 3
)

Zero values — every variable is initialized to its zero value. Critical for networking:

Exercise: Network Unit Converter

package main

import "fmt"

type ByteUnit int64

const (
    Byte     ByteUnit = 1
    Kilobyte ByteUnit = 1024
    Megabyte ByteUnit = 1024 * 1024
    Gigabyte ByteUnit = 1024 * 1024 * 1024
)

type DurationUnit int64

const (
    Millisecond DurationUnit = 1
    Second      DurationUnit = 1000
    Minute      DurationUnit = 60 * 1000
)

func convertBytes(value int64, from, to ByteUnit) float64 {
    return float64(value) * float64(from) / float64(to)
}

func main() {
    fmt.Printf("1 GB = %.0f MB\n", convertBytes(1, Gigabyte, Megabyte))
    fmt.Printf("512 MB = %.2f GB\n", convertBytes(512, Megabyte, Gigabyte))
    fmt.Printf("100 Mbps link: %.0f KB/s max throughput\n",
        convertBytes(100*1_000_000/8, Byte, Kilobyte))
}

Real-World Context

When your team sets MaxRequestBodySize = 10MB, that's ByteUnit math. When you configure IdleConnTimeout = 90 * time.Second, that's duration constants. Typed constants prevent the 10 * 1024 * 1024 scattered everywhere.