pub struct MyStruct {
    x: i64
}

impl MyStruct {
    pub fn struct_function(&mut self, val: i64) {
        self.x += val;
    }
}

fn normal_function(val: i64) {
    println!( "sum -> {}", val + 1);
}

fn do_something_with_a_function(f: fn(i64)) {
    f(23);
}

fn main() {
    // This works as you'd expect
    do_something_with_a_function(normal_function as fn(i64));

    // What I'd like to do
    // This attempts to use a closure, but throws an error.
    let instance = MyStruct{x: 0};
    let instance_function = |val: i64|{instance.struct_function(val)};
    do_something_with_a_function(instance_function as fn(i64));
}