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Puzzle 17: Explanation

Puzzle 17: Explanation

Let's learn how vectors work in Rust.

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fn main() {
    let mut my_vec = Vec::with_capacity(1);
    my_vec.push("Hello");
    println!("{}", my_vec.capacity());
    
    my_vec.push("World");
    println!("{}", my_vec.capacity());
}

Explanation

Vectors contain two components: a length indicating how many elements (items) are stored within the vector and a buffer of contiguous heap memory that contains the data for each of the items, one after the other. This buffer itself is often larger than the total number of elements stored within the vector.

Vectors are a lot like arrays, but they have a variable size. We can create a vector with a capacity of zero using new. We can create a vector with a user-specified capacity using with_capacity. The capacity represents the total size of the vector.

When we add an item to a vector, the vector checks to see if the length—number of actual items in the vector—is less than the vector’s capacity. If it is, then adding to the vector is ...