Learning Rust

Returning a closure

As threads within Rust use a return from a closure, it makes sense for us to consider that it is entirely possible to return a closure. However, returning a closure is not as straightforward as you'd expect.

Let's consider a normal function first:

fn add_five(x : i32) -> i32  
{ 
    return x + 5; 
} 
fn main() 
{ 
    let test = add_five(5); 
    println!("{}", test); 
} 

This will output the value 10. It's not rocket science. Let's change this to a closure:

fn add_five_closure() ->(Fn(i32)->i32) 
{ 
    let num = 5; 
    |x| x + num 
} 
fn main() 
{ 
    let test = add_five_closure(); 
    let f = test(5); 
    println!("{}", f); 
} 

The code for the example can be found in Chapter 11/return_closure_one.

When we run this, though, we don't get the expected answer of ...