Lifetime of reference taken for parameter vs lifetime of function resolution

[serpent]

In an example like

struct Foo
{
  n: u8
}

impl Foo {
  fn get(&self) -> u8 { self.n }
  fn set(&mut self, n: u8) { self.n = n }
}

fn main()
{
  let mut f = Foo { n : 0 };
  f.set(f.get() + 1);
}

one can't get and set in the same function call. (If the f.get() is placed in a temporary variable, then of course this works, but this is such a common idiom that I would think Rust should avoid requiring that).

I wonder if this could be improved? It seems like, if the borrow of the f.get() happens first, before the f.set, then it would be possible.

[pcwalton]

Dupe of #6268