Slice and array relationship in Go - Step-by-Step Execution

Concept Flow - Slice and array relationship

Declare array with fixed size

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Create slice referencing array

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Modify slice element

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Array element changes too

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Modify array element

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Slice element changes too

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Slice length and capacity tracked

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Slice can be resliced within capacity

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End

This flow shows how a slice points to an underlying array, so changes in one reflect in the other, and how slice length and capacity control access.

Execution Sample

Go

arr := [5]int{10, 20, 30, 40, 50}
slice := arr[1:4]
slice[0] = 25
arr[2] = 35

Create an array and a slice from it, then modify elements via slice and array to see shared data.

Execution Table

Step	Operation	Array State	Slice State (elements)	Length	Capacity	Notes
1	Declare array	[10 20 30 40 50]	N/A	N/A	N/A	Array created with 5 elements
2	Create slice arr[1:4]	[10 20 30 40 50]	[20 30 40]	3	4	Slice points to array elements 1 to 3
3	Modify slice[0] = 25	[10 25 30 40 50]	[25 30 40]	3	4	Change via slice updates array at index 1
4	Modify arr[2] = 35	[10 25 35 40 50]	[25 35 40]	3	4	Change via array updates slice element at index 1
5	Reslice slice = slice[1:3]	[10 25 35 40 50]	[35 40]	2	3	Slice resliced within capacity
6	Modify slice[1] = 45	[10 25 35 45 50]	[35 45]	2	3	Change via slice updates array at index 3
7	End	[10 25 35 45 50]	[35 45]	2	3	Final states

💡 Execution ends after slice and array modifications demonstrating shared underlying data.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	Final
arr	[10 20 30 40 50]	[10 20 30 40 50]	[10 25 30 40 50]	[10 25 35 40 50]	[10 25 35 40 50]	[10 25 35 45 50]	[10 25 35 45 50]
slice	N/A	[20 30 40]	[25 30 40]	[25 35 40]	[35 40]	[35 45]	[35 45]
len(slice)	N/A	3	3	3	2	2	2
cap(slice)	N/A	4	4	4	3	3	3

Key Moments - 3 Insights

Why does changing slice[0] also change arr[1]?

Because the slice points to the same underlying array starting at arr[1], so modifying slice[0] changes arr[1] as shown in step 3 of the execution_table.

What happens if we reslice beyond the capacity?

You get a runtime panic. In step 5, we resliced within capacity (3), so it's safe. Trying beyond capacity would cause an error.

Does changing the array affect the slice?

Yes, because the slice references the array's memory. Step 4 shows arr[2] changed, and slice[1] reflects that change.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the value of arr after modifying slice[0]?

A [10 25 35 40 50]

B [10 25 30 40 50]

C [10 20 30 40 50]

D [25 20 30 40 50]

💡 Hint

Check the 'Array State' column at step 3 in execution_table.

At which step does the slice length change from 3 to 2?

A Step 6

B Step 4

C Step 5

D Step 7

💡 Hint

Look at the 'Length' column in execution_table between steps 4 and 6.

If we modify arr[3] after step 6, what slice element changes?

A slice[1]

B slice[0]

C slice[2]

D No slice element changes

💡 Hint

Refer to the slice's underlying array indices and capacity in variable_tracker.

Concept Snapshot

Array is fixed size; slice is a view into array.
Slice has length and capacity.
Changing slice elements changes array and vice versa.
Slice can be resliced within capacity.
Slices share underlying array memory.

Full Transcript

We start by declaring an array with 5 integers. Then we create a slice that references part of this array. When we change an element in the slice, the corresponding array element changes too because they share the same memory. Similarly, changing the array updates the slice. The slice has a length and capacity that control how much of the array it can access. We can reslice within the capacity to change the slice's view. This shows the close relationship between slices and arrays in Go.