good good study, day day up!

vendor/gopl.io/ch5/sum/main.go

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+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// See page 142.
+
+// The sum program demonstrates a variadic function.
+package main
+
+import "fmt"
+
+//!+
+func sum(vals ...int) int {
+	total := 0
+	for _, val := range vals {
+		total += val
+	}
+	return total
+}
+
+//!-
+
+func main() {
+	//!+main
+	fmt.Println(sum())           //  "0"
+	fmt.Println(sum(3))          //  "3"
+	fmt.Println(sum(1, 2, 3, 4)) //  "10"
+	//!-main
+
+	//!+slice
+	values := []int{1, 2, 3, 4}
+	fmt.Println(sum(values...)) // "10"
+	//!-slice
+}