function pointer
A value that points to a named function, written with the type fn(i32) -> i32.
A function pointer (fn type) refers to a function or a closure that captures nothing; it implements all three Fn traits.
Examples
let f: fn(i32) -> i32 = double;stores a named function, andlet g: fn(i32) -> i32 = |x| x + 1;works too because that closure captures nothing.
See also