Slice creation in Go - Step-by-Step Execution

Concept Flow - Slice creation

Declare slice variable

↓

Allocate underlying array

↓

Set slice length and capacity

↓

Slice ready to use

↓

Access or modify elements

Creating a slice involves declaring it, allocating an underlying array, setting its length and capacity, then using it to access or modify elements.

Execution Sample

Go

package main
import "fmt"
func main() {
  s := make([]int, 3, 5)
  fmt.Println(s)
}

This code creates a slice of integers with length 3 and capacity 5, then prints it.

Execution Table

Step	Action	Slice Length	Slice Capacity	Underlying Array Size	Output
1	Declare slice variable s	0	0	0
2	Call make([]int, 3, 5)	3	5	5
3	Slice s created with length 3, capacity 5	3	5	5
4	Print slice s	3	5	5	[0 0 0]

💡 Slice s is created with length 3 and capacity 5; printing shows default zero values.

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
s	nil	slice with len=3 cap=5	slice with len=3 cap=5	slice with len=3 cap=5

Key Moments - 2 Insights

Why does the slice print show three zeros instead of five?

Because the slice length is 3, only the first 3 elements are accessible and printed, even though capacity is 5 (see execution_table step 4).

What is the difference between slice length and capacity?

Length is how many elements the slice currently holds (step 3), capacity is the total space allocated in the underlying array (step 2).

Visual Quiz - 3 Questions

Look at the execution_table at step 2, what is the capacity of slice s?

A 0

B 3

C 5

D nil

💡 Hint

Check the 'Slice Capacity' column at step 2 in execution_table.

At which step does the slice s get its length set to 3?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Slice Length' column in execution_table to see when length changes from 0 to 3.

If we change make([]int, 3, 5) to make([]int, 5, 5), what will be the output at step 4?

A [0 0 0]

B [0 0 0 0 0]

C []

D nil

💡 Hint

The output shows elements equal to the slice length; see how length affects output in execution_table step 4.

Concept Snapshot

Slice creation in Go:
- Use make([]Type, length, capacity)
- Length = accessible elements
- Capacity = underlying array size
- Default values are zero
- Printing shows elements up to length

Full Transcript

In Go, creating a slice involves declaring a slice variable and using the make function to allocate an underlying array with a specified length and capacity. The length determines how many elements are accessible and printed, while the capacity is the total allocated space. For example, make([]int, 3, 5) creates a slice with length 3 and capacity 5. When printed, only the first 3 elements show, initialized to zero. Understanding the difference between length and capacity helps manage slices effectively.