What is monomorphization

Monomorphization is the Rust compiler's process of generating specific, optimized code for each type used with a generic function or struct at compile time.

Monomorphization is the process where the Rust compiler generates a separate, concrete version of a generic function or struct for each specific type used at compile time. Instead of passing type information at runtime, the compiler replaces the generic placeholder T with the actual type (like i32 or char) to create optimized, type-specific code. For example, calling largest with a slice of i32 and a slice of char results in two distinct functions in the final binary, one for each type.

fn largest<T: PartialOrd>(list: &[T]) -> &T {
    let mut largest = &list[0];
    for item in list {
        if item > largest {
            largest = item;
        }
    }
    largest
}

// Compiler generates: largest_i32 and largest_char
let max_i32 = largest(&[1, 2, 3]);
let max_char = largest(&['a', 'b', 'c']);

Monomorphization is like a factory that builds a custom tool for every specific job you ask it to do, rather than using one generic tool for everything. When you use a generic function with different data types, the compiler creates a unique, optimized version of that function for each type before your program even runs. This ensures your code runs as fast as if you had written separate functions for every single type manually.