How to Use Enum Variants as Function Pointers

You cannot use enum variants directly as function pointers because they are not functions. Instead, define an enum where each variant holds a function pointer, then match on the enum to call the correct function.

fn add(a: i32, b: i32) -> i32 { a + b }
fn sub(a: i32, b: i32) -> i32 { a - b }

enum Operation {
    Add(fn(i32, i32) -> i32),
    Sub(fn(i32, i32) -> i32),
}

fn main() {
    let op = Operation::Add(add);
    match op {
        Operation::Add(f) => println!("{}", f(2, 3)),
        Operation::Sub(f) => println!("{}", f(2, 3)),
    }
}

Enum variants are just labels for data, not executable code, so you cannot point to them like a function. Think of an enum as a menu of options, while a function pointer is a specific instruction on how to cook a dish. You must store the actual instruction (the function) inside the menu item (the enum variant) to execute it later.