68 lines
2.3 KiB
Markdown
68 lines
2.3 KiB
Markdown
# The Mechanics of Append Quiz
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## Which append call below allocates a new backing array for the following slice?
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```go
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words := []string{"lucy", "in", "the", "sky", "with", "diamonds"}
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```
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1. words = append(words[:3], "crystals")
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2. words = append(words[:4], "crystals")
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3. words = append(words[:5], "crystals")
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4. words = append(words[:5], "crystals", "and", "diamonds") *CORRECT*
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> **1:** No, it just overwrites the 4th element.
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>
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> **2:** No, it just overwrites the 5th element.
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>
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> **3:** No, it just overwrites the last element.
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>
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> **4:** Yes, it overwrites the last element, then it adds two element. However, there is not enough space to do that, so it allocates a new backing array.
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## What does the program print?
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```go
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words := []string{"lucy", "in", "the", "sky", "with", "diamonds"}
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words = append(words[:1], "is", "everywhere")
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words = append(words, words[len(words)+1:cap(words)]...)
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```
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1. lucy in the sky with diamonds
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2. lucy is everywhere in the sky with diamonds
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3. lucy is everywhere with diamonds *CORRECT*
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4. lucy is everywhere
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> **3:** line #2 overwrites the 2nd and 3rd elements. line #3 appends ["with" "diamonds"] after the ["lucy" "is" "everwhere"].
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## What are the length and capacity of the words slice?
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```go
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// The words slice has 1023 elements.
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//
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// Tip: The keyed slice works like the same as a keyed array.
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// If you don't remember how it works, please check out the keyed elements in the arrays section.
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//
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words := []string{1022: ""}
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words = append(words, "boom!")
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```
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1. Length: 1024 - Capacity: 1024
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2. Length: 1025 - Capacity: 1025
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3. Length: 1025 - Capacity: 1280
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4. Length: 1024 - Capacity: 2048 *CORRECT*
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> **4:** That's right! Append function grows by doubling the capacity of the previous slice.
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## What are the length and capacity of the words slice?
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```go
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// The words slice has 1024 elements.
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//
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// Tip: The keyed slice works like the same as a keyed array.
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// If you don't remember how it works, please check out the keyed elements in the arrays section.
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//
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words := []string{1023: ""}
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words = append(words, "boom!")
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```
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1. Length: 1024 - Capacity: 1024
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2. Length: 1025 - Capacity: 1025
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3. Length: 1025 - Capacity: 1280 *CORRECT*
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4. Length: 1025 - Capacity: 2048
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> **3, 4:** After 1024 elements, the append function grows at a slower rate, about 25%. |