在rust中，move对作为引用的变量做了什么？

Question

I have a function that composes (or pipes?) multiple functions into a single one:

fn compose<'a, T>(fns: &'a [&dyn Fn(T) -> T]) -> Box<dyn Fn(T) -> T + 'a> {
  // Why do I need to move fns here?
  // If I don't put move, I get the following error:
  // to force the closure to take ownership of `fns` (and any other referenced variables), use the `move` keyword: `move `
  Box::new(move |mut x| {
    for f in fns {
      x = f(x);
    }
    x
  })
}

I don't get why I need to move the fns into the closure when it's just a reference. What does move actually do here?

Answer 1

A reference is just a normal variable, like any other variable. If you don't move , your fns inside the closure will be a reference to a reference, which goes out of scope at the end of the function.