Primitives

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

  1. Scalar Types
  2. Compound Types

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
  • and 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.

Variables can be type annotated or inferre from context

 
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;
}
  1. Variables can be type annotated, or a default will be used.
  2. A type can also be inferred from context
  3. A mutable variable’s value can be changed.
  4. The type of a variable can’t be changed.
  5. Variables can be overwritten with shadowing.

See also:

the std library, mut, inference, and shadowing