Slice Programs

Learn slice programs through an executable example, then connect the small demonstration to production code.

Slices provide flexible views into arrays. Practice filtering, appending, copying and capacity behavior with meaningful collections.

The example builds a new slice containing even values, leaving the original input unchanged.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import "fmt"

func filterEven(values []int) []int {
	result := make([]int, 0, len(values))
	for _, n := range values {
		if n%2 == 0 {
			result = append(result, n)
		}
	}
	return result
}
func main() {
	numbers := []int{1, 2, 3, 4, 6}
	fmt.Println("Even:", filterEven(numbers))
	fmt.Println("Original:", numbers)
}

Output

Even: [2 4 6]
Original: [1 2 3 4 6]

Each value is tested with remainder by two. The result contains 2, 4 and 6, while the input retains all five values.

• Appending to a slice may reuse or replace its backing array depending on capacity.
• Do not assume an assignment copies all slice elements; use copy or slices.Clone when an independent copy is needed.

Create a filter for numbers greater than three and compare the original and new slices.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Slice Programs in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.