slice pitfall

Capacity pitfall.go

package main

import "fmt"

func main() {
	a := [5]int{1, 2, 3, 4, 5}
	s1 := a[0:3] // len=3 cap=5
	s2 := a[3:5] // len=2 cap=2

	fmt.Println("initial a  :", a)   // [1 2 3 4 5]
	fmt.Println("initial s1  :", s1) // [1 2 3 4 5]
	fmt.Println("initial s2 :", s2)  // [4 5]

	s1 = append(s1, 100) // within cap → overwrites a[3]
	fmt.Println("\nafter append(s1,100):")
	fmt.Println("s1  :", s1) // [1 2 3 100 5]
	fmt.Println("a  :", a)   // [1 2 3 100 5]
	fmt.Println("s2 :", s2)  // [100 5]  ← overwritten!
}