Rust pointers, boxing/heap

pointer.rs

// Pretend this is an actual big struct in which it would be
// expensive to copy by value.
struct BigStruct {
    one: int,
    two: int,
    // etc
    one_hundred: int,
}

// An antipattern would be for the return type to be
// Box<BigStruct> where Box denotes it's on the heap.
fn foo(x: Box<BigStruct>) -> BigStruct {
    return *x;
}

fn main() {
    let x = box BigStruct {
        one: 1,
        two: 2,
        one_hundred: 100,
    };

    // Rust knows to not copy this value due to the "box"
    // prefix.
    //
    // This allows the caller to choose how they want to use
    // the output
    //
    // For example
    //
    // let y = foo(x);
    //
    // would produce a copy.
    let y = foo(x);
}