Maps

A map stores values under keys instead of numbered positions — Go's equivalent of a dictionary in Python or an object used as a lookup table in JavaScript.

Creating and reading a map

package main

import "fmt"

func main() {
	prices := map[string]float64{
		"apple":  0.5,
		"banana": 0.3,
	}

	fmt.Println(prices["apple"])
	prices["cherry"] = 2.0
	fmt.Println(prices)
}

0.5
map[apple:0.5 banana:0.3 cherry:2]

map[string]float64 is a map with string keys and float64 values. Reading a key looks just like indexing a slice; adding a new key is a plain assignment, no separate "insert" method required.

Missing keys and the comma-ok idiom

Reading a key that isn't in the map doesn't panic or error — it just gives you the zero value for the map's value type, which can be genuinely ambiguous. The comma-ok form tells the two cases apart:

package main

import "fmt"

func main() {
	stock := map[string]int{"apple": 0, "banana": 12}

	value, ok := stock["apple"]
	fmt.Println(value, ok)

	value, ok = stock["cherry"]
	fmt.Println(value, ok)
}

0 true
0 false

Both lookups print 0 for the value, but ok tells you why: "apple" is genuinely in the map with a stock count of 0, while "cherry" isn't in the map at all and 0 is just the zero value Go handed back. Without checking ok, those two very different situations would look identical.

Deleting a key and iterating

package main

import "fmt"

func main() {
	ages := map[string]int{"Priya": 29, "Sam": 34}
	delete(ages, "Sam")

	for name, age := range ages {
		fmt.Println(name, age)
	}
}

Priya 29

delete(ages, "Sam") removes that key entirely, and for name, age := range ages walks every remaining key/value pair. Unlike a slice, a Go map makes no promise about iteration order — running this same code again could print entries in a different order if there were more of them.