Slices

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Goal

Hold an ordered list of values. After this page you will have the []Item the endpoint returns.

Prerequisites

• Structs

Slice vs array

Go has two list-like types. An array has a fixed length baked into its type — [3]int is different from [4]int. A slice is a view over an array, with variable length. You almost always want a slice.

Write a slice type as []T — for example, []int, []string, []Item.

For everything slices can do, see the Go blog post on slices. The two operations we need now are slice-literal construction and append.

Code

package main

import "fmt"

type Item struct {
	ID    int
	Name  string
	Price float64
}

func main() {
	// Slice literal — three items, length 3.
	items := []Item{
		{ID: 1, Name: "Notebook", Price: 4.0},
		{ID: 2, Name: "Pen", Price: 2.5},
		{ID: 3, Name: "Sticker pack", Price: 5.0},
	}

	fmt.Println("count:", len(items))

	for _, item := range items {
		fmt.Printf("%d %s $%.2f\n", item.ID, item.Name, item.Price)
	}

	// Append a fourth item — append returns a new slice.
	items = append(items, Item{ID: 4, Name: "Eraser", Price: 1.0})
	fmt.Println("count after append:", len(items))
}

Run it:

go run main.go

Output:

count: 3
1 Notebook $4.00
2 Pen $2.50
3 Sticker pack $5.00
count after append: 4

len returns the current length. append returns a new slice — you must reassign the result, even when you use the same variable name.

For frontend developers

A slice is the closest Go has to a JS array. The big difference: a slice's element type is fixed at compile time. []Item only holds Item values, never strings.

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