Module 2: Maps (The Key Rack)

📚 Module 2: Maps

Course ID: GO-106
Subject: The Key Rack

A Map allows you to store data in Key-Value pairs. It is the most efficient way to find something instantly without searching through a list.

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🏗️ Step 1: Instant Retrieval

🧩 The Analogy: The Hotel Key Rack

• The Key: The Room Number (e.g., “301”).
• The Value: The physical key to that room.
• If you ask for room “301,” the receptionist doesn’t check every room in the hotel. They look at the Key Rack and grab it instantly.

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🏗️ Step 2: In Code

// 1. Create a map of [Name] to [Age]
ages := make(map[string]int)

// 2. Add some data
ages["Alice"] = 25
ages["Bob"] = 30

// 3. Get data back
aliceAge := ages["Alice"]

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🏗️ Step 3: Checking if a Key Exists

In Go, if you ask for a key that isn’t there, you get a Zero Value (Module 2). But what if the value actually is zero? We use the “Comma OK” pattern.

val, ok := ages["Charlie"]
if ok {
    fmt.Println("Found Charlie!", val)
} else {
    fmt.Println("Charlie doesn't exist.")
}

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🥅 Module 2 Review

1. Map: A Key-Value dictionary.
2. make(): The required tool to build a new map.
3. OK Pattern: How we check if a key actually exists.

:::tip Senior Tip Maps in Go are NOT sorted. If you print a map twice, the order might change! If you need a specific order, you must sort the keys separately. :::