primitives.md

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.

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;

    /* Compound types - Array and Tuple */

    // Array signature consists of Type T and length as [T; length].
    let my_array: [i32; 5] = [1, 2, 3, 4, 5];

    // Tuple is a collection of values of different types 
    // and is constructed using parentheses ().
    let my_tuple = (5u32, 1u8, true, -5.04f32);
}

See also:

the std library, mut, inference, and shadowing