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example2.go
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example2.go
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// Copyright 2014 Ardan Studios
//
// All material is licensed under the Apache License Version 2.0, January 2004
// http://www.apache.org/licenses/LICENSE-2.0
// Sample program to show how maps behave when you read an
// absent key.
package main
import "fmt"
func main() {
// Create a map to track scores for players in a game.
scores := make(map[string]int)
// Read the element at key "anna". It is absent so we get
// the zero-value for this map's value type.
score := scores["anna"]
fmt.Println("Score:", score)
// If we need to check for the presence of a key we use
// a 2 variable assignment. The 2nd variable is a bool.
score, ok := scores["anna"]
fmt.Println("Score:", score, "Present:", ok)
// We can leverage the zero-value behavior to write
// convenient code like this:
scores["anna"]++
// Without this behavior we would have to code in a
// defensive way like this:
if n, ok := scores["anna"]; ok {
scores["anna"] = n + 1
} else {
scores["anna"] = 1
}
score, ok = scores["anna"]
fmt.Println("Score:", score, "Present:", ok)
}
// Outputs:
// Score: 0
// Score: 0 Present: false
// Score: 2 Present: true