Core Collections: Slices ([]T), Maps (map[K]V) & Structs

1Concept

A Slice is a 3-word header (pointer to backing array, length, capacity). Calling append() grows capacity automatically. A Map provides O(1) hash lookups.

2Architecture Diagram

Slice Header: [ Pointer (8-byte) | Length (8-byte) | Capacity (8-byte) ]
                     │
                     ▼
         Backing Array: [ 10 ] [ 20 ] [ 30 ] [ ... ]

3Code Example

package main

import "fmt"

func main() {
    // Dynamic Slice
    numbers := make([]int, 0, 4) // len 0, cap 4
    numbers = append(numbers, 10, 20, 30)
    fmt.Printf("Slice: %v, Len: %d, Cap: %d\n", numbers, len(numbers), cap(numbers))

    // Hash Map
    cache := make(map[string]int)
    cache["session_101"] = 1500
    cache["session_102"] = 2800

    if val, exists := cache["session_101"]; exists {
        fmt.Printf("Cache Hit: %d\n", val)
    }
}

4Expected Output

Slice: [10 20 30], Len: 3, Cap: 4
Cache Hit: 1500

5Key Takeaways

• ✓Pre-allocate slice capacity with make([]T, 0, cap) to avoid reallocations.
• ✓Reading a missing key in a Go map returns the type's zero-value (use 'val, ok := map[key]').
• ✓Maps in Go are not thread-safe for concurrent writes (use sync.RWMutex or sync.Map).