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This adds strictly more information to the source files and reduces the need for customized tooling to render the book. (While this should not change the output of _rustbook_, it is very useful when rendering the sources with external tools like Pandoc.)
61 lines
1.4 KiB
Markdown
61 lines
1.4 KiB
Markdown
% Vectors
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A ‘vector’ is a dynamic or ‘growable’ array, implemented as the standard
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library type [`Vec<T>`][vec]. The `T` means that we can have vectors
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of any type (see the chapter on [generics][generic] for more).
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Vectors always allocate their data on the heap.
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You can create them with the `vec!` macro:
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```rust
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let v = vec![1, 2, 3, 4, 5]; // v: Vec<i32>
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```
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(Notice that unlike the `println!` macro we’ve used in the past, we use square
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brackets `[]` with `vec!` macro. Rust allows you to use either in either situation,
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this is just convention.)
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There’s an alternate form of `vec!` for repeating an initial value:
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```rust
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let v = vec![0; 10]; // ten zeroes
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```
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## Accessing elements
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To get the value at a particular index in the vector, we use `[]`s:
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```rust
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let v = vec![1, 2, 3, 4, 5];
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println!("The third element of v is {}", v[2]);
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```
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The indices count from `0`, so the third element is `v[2]`.
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## Iterating
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Once you have a vector, you can iterate through its elements with `for`. There
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are three versions:
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```rust
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let mut v = vec![1, 2, 3, 4, 5];
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for i in &v {
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println!("A reference to {}", i);
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}
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for i in &mut v {
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println!("A mutable reference to {}", i);
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}
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for i in v {
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println!("Take ownership of the vector and its element {}", i);
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}
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```
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Vectors have many more useful methods, which you can read about in [their
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API documentation][vec].
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[vec]: ../std/vec/index.html
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[generic]: generics.html
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