how to initialize a let based on conditional branches

gistfile1.txt

// i often do this just so i can make a variable a constant let and not a var;
// with a var I could just use a switch, but it's better to have a let when possible

// how to make this prettier?

let someConstant: Int64 =
                someBoolExpression ? 1 :
                someOtherBoolExpression ? 2 : 
                yetAnotherBoolExpression ? 3 : 0
                
               // or perhaps this style of code is just acceptable?

let x: Int
if condition {
    x = 3
} else {
    x = 5
}

and

let foo = {
    switch (a, b, c) {
    case (true, true, _):
        return 1
     case (false, _, _):
         return 2
    ...
    }
}()