learngo/16-slices/questions/6-capacity.md

Capacity and Append Mechanics Quiz

What is the difference between the length and capacity of a slice?

1. They are the same
2. The length is always greater than the capacity
3. The capacity is always greater than the capacity
4. The length describes the length of a slice but a capacity describes the length of the backing array beginning from the first element of the slice CORRECT

2: The length is never greater than the capacity.

3: The length and capacity of a slice can be equal.

What is the capacity of a nil slice?

1. It is equal to its length + 1
2. It is nil
3. 0 CORRECT
4. 1

2: The capacity's type is int, it cannot be nil.

What are the length and capacity of the slice value?

[]string{"I", "have", "a", "great", "capacity"}

1. Length: 5 - Capacity: 5 CORRECT
2. Length: 0 - Capacity: 5
3. Length: 5 - Capacity: 10
4. Length: 10 - Capacity: 10

1: That's right! A slice literal creates a new slice value with equal length and capacity.

What are the length and capacity of the 'words' slice?

words := []string{"lucy", "in", "the", "sky", "with", "diamonds"}
words = words[:0]

1. Length: 0 - Capacity: 0
2. Length: 6 - Capacity: 6
3. Length: 0 - Capacity: 6 CORRECT
4. Length: 5 - Capacity: 10

3: Right! words[:0] slices for 0 elements, which in turn returns a slice with zero-length. Because the words slice points to the same backing array, its capacity is equal to 6.

What are the length and capacity of the 'words' slice?

words := []string{"lucy", "in", "the", "sky", "with", "diamonds"}
words = words[0:]

1. Length: 0 - Capacity: 0
2. Length: 6 - Capacity: 6 CORRECT
3. Length: 0 - Capacity: 6
4. Length: 5 - Capacity: 10

2: Right! words[0:] slices for the rest of the elements, which in turn returns a slice with the same length as the original slice: 6. Beginning from the first array element, the words slice's backing array contains 6 elements; so its capacity is also 6.

What are the length and capacity of the 'words' slice?

words := []string{"lucy", "in", "the", "sky", "with", "diamonds"}
words = words[2:cap(words)-2]

1. Length: 4 - Capacity: 6
2. Length: 6 - Capacity: 4
3. Length: 2 - Capacity: 6
4. Length: 2 - Capacity: 4 CORRECT

4: Right! words[2:cap(words)-2] is equal to words = words[2:4], so it returns: ["the" "sky"]. So, its length is 2. But there are 4 more elements (["the" "sky" "with" "diamonds"]) in the backing array, so the capacity is 4.