Slice length and capacity in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the length of a slice represent in Go?

The length of a slice is the number of elements it currently holds. It tells you how many items you can access safely.

beginner

What does the capacity of a slice represent in Go?

The capacity of a slice is the total number of elements the slice can hold in its underlying array before it needs to allocate more memory.

beginner

How do you get the length and capacity of a slice named s in Go?

Use the built-in functions: len(s) gives the length, and cap(s) gives the capacity.

intermediate

If you create a slice with make([]int, 3, 5), what are its length and capacity?

Length is 3 because you asked for 3 elements initially. Capacity is 5 because the underlying array can hold up to 5 elements before resizing.

intermediate

What happens to the capacity of a slice when you append elements beyond its current capacity?

Go automatically creates a new underlying array with larger capacity, copies the existing elements, and appends the new ones. The capacity grows, usually doubling to reduce future allocations.

What does len(s) return for a slice s in Go?

A The size in bytes of the slice

B The number of elements currently in the slice

C The total capacity of the slice

D The memory address of the slice

len(s) returns how many elements are currently in the slice.

What does cap(s) return for a slice s in Go?

A The total capacity of the slice's underlying array

B The number of elements currently in the slice

C The length of the slice plus one

D The number of bytes used by the slice

cap(s) returns the capacity, which is the size of the underlying array that the slice can use.

If you create a slice with make([]int, 4, 10), what is the length and capacity?

A Length 10, Capacity 4

B Length 10, Capacity 10

C Length 4, Capacity 4

D Length 4, Capacity 10

The first number is length, the second is capacity.

What happens when you append an element to a slice that is already at full capacity?

A The program crashes

B The slice silently ignores the append

C Go allocates a new underlying array with larger capacity and copies elements

D The slice length decreases

Go automatically grows the slice's capacity by allocating a new array and copying elements.

Which built-in function do you use to find the capacity of a slice?

A cap()

B len()

C size()

D capacity()

cap() returns the capacity of a slice.

Explain the difference between the length and capacity of a slice in Go.

Think about how many elements you can use now versus how many you can add before resizing.

Describe what happens internally when you append an element to a slice that has reached its capacity.

Imagine your backpack is full and you get a bigger one to carry more stuff.