# Primitives

Rust provides access to a wide variety of `primitives`. A sample includes:

### Scalar Types

* Signed integers: `i8`, `i16`, `i32`, `i64`, `i128` and `isize` (pointer size)
* Unsigned integers: `u8`, `u16`, `u32`, `u64`, `u128` and `usize` (pointer
  size)
* Floating point: `f32`, `f64`
* `char` Unicode scalar values like `'a'`, `'α'` and `'∞'` (4 bytes each)
* `bool` either `true` or `false`
* The unit type `()`, whose only possible value is an empty tuple: `()`

Despite the value of a unit type being a tuple, it is not considered a compound
type because it does not contain multiple values.

### Compound Types

* Arrays like `[1, 2, 3]`
* Tuples like `(1, true)`

Variables can always be *type annotated*. Numbers may additionally be annotated
via a *suffix* or *by default*. Integers default to `i32` and floats to `f64`.
Note that Rust can also infer types from context.

```rust,editable,ignore,mdbook-runnable
fn main() {
    // Variables can be type annotated.
    let logical: bool = true;

    let a_float: f64 = 1.0;  // Regular annotation
    let an_integer   = 5i32; // Suffix annotation

    // Or a default will be used.
    let default_float   = 3.0; // `f64`
    let default_integer = 7;   // `i32`

    // A type can also be inferred from context.
    let mut inferred_type = 12; // Type i64 is inferred from another line.
    inferred_type = 4294967296i64;

    // A mutable variable's value can be changed.
    let mut mutable = 12; // Mutable `i32`
    mutable = 21;

    // Error! The type of a variable can't be changed.
    mutable = true;

    // Variables can be overwritten with shadowing.
    let mutable = true;
}
```

### See also:

[the `std` library][std], [`mut`][mut], [`inference`][inference], and
[`shadowing`][shadowing]

[std]: https://doc.rust-lang.org/std/
[mut]: variable_bindings/mut.md
[inference]: types/inference.md
[shadowing]: variable_bindings/scope.md
