src/doc/rust-by-example/src/primitives.md

   1 # Primitives
   2
   3 Rust provides access to a wide variety of `primitives`. A sample includes:
   4
   5
   6 ### Scalar Types
   7
   8 * signed integers: `i8`, `i16`, `i32`, `i64`, `i128` and `isize` (pointer size)
   9 * unsigned integers: `u8`, `u16`, `u32`, `u64`, `u128` and `usize` (pointer
  10   size)
  11 * floating point: `f32`, `f64`
  12 * `char` Unicode scalar values like `'a'`, `'α'` and `'∞'` (4 bytes each)
  13 * `bool` either `true` or `false`
  14 * and the unit type `()`, whose only possible value is an empty tuple: `()`
  15
  16 Despite the value of a unit type being a tuple, it is not considered a
  17 compound type because it does not contain multiple values.
  18
  19 ### Compound Types
  20
  21 * arrays like `[1, 2, 3]`
  22 * tuples like `(1, true)`
  23
  24 Variables can always be *type annotated*. Numbers may additionally be
  25 annotated via a *suffix* or *by default*. Integers default to `i32` and
  26 floats to `f64`. Note that Rust can also infer types from context.
  27
  28 ```rust,editable,ignore,mdbook-runnable
  29 fn main() {
  30     // Variables can be type annotated.
  31     let logical: bool = true;
  32
  33     let a_float: f64 = 1.0;  // Regular annotation
  34     let an_integer   = 5i32; // Suffix annotation
  35
  36     // Or a default will be used.
  37     let default_float   = 3.0; // `f64`
  38     let default_integer = 7;   // `i32`
  39
  40     // A type can also be inferred from context
  41     let mut inferred_type = 12; // Type i64 is inferred from another line
  42     inferred_type = 4294967296i64;
  43
  44     // A mutable variable's value can be changed.
  45     let mut mutable = 12; // Mutable `i32`
  46     mutable = 21;
  47
  48     // Error! The type of a variable can't be changed.
  49     mutable = true;
  50
  51     // Variables can be overwritten with shadowing.
  52     let mutable = true;
  53 }
  54 ```
  55
  56 ### See also:
  57
  58 [the `std` library][std], [`mut`][mut], [inference], and [shadowing]
  59
  60 [std]: https://doc.rust-lang.org/std/
  61 [mut]: variable_bindings/mut.html
  62 [inference]: types/inference.html
  63 [shadowing]: variable_bindings/scope.html