Programming Rust, 3rd Edition

Chapter 3. Fundamental Types

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The first principles of the universe are atoms and empty space; everything else is merely thought to exist.

Diogenes Laertes (describing the philosophy of Democritus)

This chapter covers Rust’s fundamental types for representing values: integer and floating-point numbers, strings and characters, vectors and arrays, and so on. These source-level types have concrete machine-level counterparts with predictable costs and performance.

Compared to a dynamically typed language like JavaScript or Python, Rust requires more planning from you up front. You must spell out the types of function arguments and return values, struct fields, and a few other constructs. For the rest, Rust’s type inference will generally figure out the types for you. For example, you could spell out every type in a function, like this:

fn grade_cutoffs(tier_size: u32) -> Vec<u32> {
    let mut cutoffs: Vec<u32> = Vec::<u32>::new();
    for tier in 1u32..5u32 {
        cutoffs.push(100u32 - tier * tier_size ...