Incidentally, I'm not personally very fond of "assigning an if-expression to a variable" since it disconnects the variable name from the value it gets. An example with two variables illustrates the point:

  let (value, weight) =             let (value, weight)
    if values.empty() {             if values.empty() {
      (0, 1.0)                        value = 0
    } else {                          weight = 1.0
      (values[0], 1/values.len())   } else {
    }                                 value = values[0]
                                      weight = 1/values.len()
                                    }

I think the right (the "old way") is more readable. However it requires the variables be mutable or declaration be separable from initialization.