Maps (Key-Value Storage, Comma-Ok Idiom & Iteration) - Go Tutorial for Beginners #10

Maps (Key-Value Storage, Comma-Ok Idiom & Iteration) in Go

Maps in Go provide a built-in hash table structure to store and retrieve data using key-value pairs efficiently. This guide covers creating maps, safely accessing elements with the comma-ok idiom, deleting entries, iterating over maps, and working with maps containing struct values.

Code

package main

import "fmt"

func main() {
  // Create and initialize a map with string keys and int values
  ages := map[string]int{
    "Alice": 25,
    "Bob":   30,
  }

  // Access a value directly
  fmt.Println("Alice's age:", ages["Alice"])

  // Use the comma-ok idiom to safely check if a key exists
  age, exists := ages["Carol"]
  if exists {
    fmt.Println("Carol's age:", age)
  } else {
    fmt.Println("Carol not found in map")
  }

  // Add or update a value
  ages["Carol"] = 22
  fmt.Println("Added Carol:", ages["Carol"])

  // Delete a key from the map
  delete(ages, "Bob")

  // Iterate over the map
  fmt.Println("Current map entries:")
  for name, age := range ages {
    fmt.Printf("%s: %d\n", name, age)
  }

  // Maps with struct values
  type Person struct {
    Age  int
    City string
  }
  people := make(map[string]Person)
  people["Dave"] = Person{Age: 40, City: "New York"}
  fmt.Println("Dave's info:", people["Dave"])
}

Key Points

• Maps are Go’s built-in hash tables for fast key-value storage and retrieval.
• The comma-ok idiom safely checks if a key exists, preventing ambiguity with zero values.
• Use the built-in delete function to remove keys from a map.
• Iterate over maps using a for-range loop to access keys and values.
• Maps can store complex data types like structs as values for richer data modeling.