Pass Generic Function as argument

Question

I would like to be able to pass a generic function to another function (in this case a closure), without losing the "genericness" of the passed function. Since tha

Answer 1

As has been mentioned, unfortunately the call is monomorphized at the call site, so you cannot pass a generic function, you can only pass a monomorphized version of the generic function.

What you can pass, however, is a function builder:

use std::fmt::Debug;

struct Builder;

impl Builder {
    fn build(&self) -> fn(I) -> I {
        fn input(x: I) -> I { x }
        input
    }
}

fn test(gen: F)
    where F: Fn(Builder) -> T
{
    let builder = Builder;
    println!("{:?}", gen(builder));
}

fn main() {
    test(|builder| {
        builder.build()(10);
        builder.build()(10.0)
    });
}

The Builder is able to generate instances of input on demand.