Rust for C-Programmers

8.8 Generics in Functions

Generics allow defining functions that work with multiple data types as long as those types satisfy certain constraints (traits). Rust supports generics in both functions and data types—topics explored in detail in Chapter 12.

8.8.1 Example: Maximum Value

A Function Without Generics

fn max_i32(a: i32, b: i32) -> i32 {
    if a > b { a } else { b }
}

A Generic Function

use std::cmp::PartialOrd;

fn max_generic<T: PartialOrd>(a: T, b: T) -> T {
    if a > b { a } else { b }
}

fn main() {
    println!("max of 5 and 10: {}", max_generic(5, 10));
    println!("max of 2.5 and 1.8: {}", max_generic(2.5, 1.8));
}

• The PartialOrd trait allows comparison with < and >.

Generics help eliminate redundant code and provide flexibility when designing APIs. The type parameter, commonly named T, is enclosed in angle brackets (<>) after the function name and serves as a placeholder for the actual data type used in function arguments. In most cases, this generic type must implement certain traits to ensure that all operations within the function are valid.

The compiler uses monomorphization to generate specialized machine code for each concrete type used with a generic function.