Go Ep 5: Maps & Hash Tables

TL;DR (Quick Summary)

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• Map (map[KeyType]ValueType): An unordered hash table. KeyType must be comparable (strings, numbers, pointers). Uninitialized maps are nil.
• Comma-OK Map Lookup: val, exists := myMap["key"]. Checks if a key actually exists without getting a false positive on zero values.
• Delete Key: delete(myMap, "key") removes a key-value pair cleanly.

1. Map Operations & Comma-OK Idiom

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package main

import "fmt"

func main() {
	// 1. Initializing a map using make()
	userRoles := make(map[string]string)

	// 2. Insert & Update
	userRoles["rachmat"] = "admin"
	userRoles["alice"] = "developer"

	// 3. Delete a key
	delete(userRoles, "alice")

	// 4. Comma-OK Lookup (Checking key existence)
	role, exists := userRoles["bob"]
	if !exists {
		fmt.Println("User 'bob' not found in map!")
	} else {
		fmt.Println("Bob's Role:", role)
	}

	// 5. Iterating over a map
	for user, r := range userRoles {
		fmt.Printf("User: %s -> Role: %s
", user, r)
	}
}

2. Troubleshooting & Common Errors

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Error 1: panic: assignment to entry in nil map

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The Cause: Writing a key to a map variable declared without initialization (var m map[string]int).

// 🔴 Dangerous: Panics!
var m map[string]int
m["key"] = 42

// 🟢 Fix: Initialize using make() or literal syntax
m := make(map[string]int)
m["key"] = 42

Summary & Next Steps

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In this episode:

• We performed CRUD operations on Go Maps and used comma-ok lookups.
• We iteration and key deletion on maps.

In Episode 6: Structs, Fields & JSON Serialization, we will master custom composite Structs!