Accessing Map Values

We can access the value corresponding to a key in a map using the following syntax:

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              1
            
mapName["keyName"]

For example:

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              1234567891011121314
            
package main
import "fmt"

func main() {
	prices := map[string]int {
		"apple": 100,
		"banana": 120,
		"peach": 170,
	}

	fmt.Println(prices["apple"]) // Output: 100
	fmt.Println(prices["banana"]) // Output: 120
	fmt.Println(prices["peach"]) // Output: 170
}

The expression prices["apple"] essentially references the memory location where the value 100 is stored; hence, it acts like a variable. Therefore, we can edit the value stored at that key using the = operator:

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              12345678910111213
            
package main
import "fmt"

func main() {
	prices := map[string]int {
		"apple": 100,
		"banana": 120,
		"peach": 170,
	}

	prices["apple"] = 160
	fmt.Println(prices["apple"]) // Output: 160
}

We can use the same assignment syntax to create a new key in the map:

If the provided keyName doesn't exist in the map, it will create and add a new key to the map with the assigned value.

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              1234567891011121314151617
            
package main
import "fmt"

func main() {
	
	numbers := map[string]int {
		"one": 1,
		"two": 2,
		"three": 3,
	}
	
	fmt.Println(numbers) // Output: map[one:1 three:3 two:2]
	
	numbers["four"] = 4
	
	fmt.Println(numbers) // Output: map[four:4 one:1 three:3 two:2]
}

Tudo estava claro?

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Seção 6. Capítulo 6