arithmetic within string literal in Swift

Question

Playing with Swift, I found something awkward error.

let cost = 82.5
let tip = 18.0
let str = "Your total cost will be \(cost + tip)"

This works fine as I expect, but

let cost = 82.5
let tip:Float = 18
let str = "Your total cost will be \(cost + tip)"

would not work with error

could not find member 'convertFromStringInterpolationSegment' 
let str = "Your total cost will be \(cost + tip)"

The difference between two example is declaring tip constant to explicitly float or not. Would this be reasonable result?

Answer 1

You still need to cast the numbers into the same type so they can be added together, eg:

let cost = 82.5
let tip:Float = 18
let str = "Your total cost will be \(Float(cost) + tip)"

By default real number literals are inferred as Double , ie:

let cost:Double = 82.5

So they need to be either explicitly cast to a Double or a Float to be added together.

Answer 2

Values are never implicitly converted to another type.

let cost = 82.5
let tip:Float = 18
let str = "Your total cost will be \(cost + tip)"

In the above example it is considering cost as double & you have defined tip as float, so it is giving error.

Rather specify the type of cost as float as shown below

let cost:Float = 82.5

Hope it will solve your problem.

Answer 3

In your code cost in inferred to be of type Double .

In your first (working) example tip is also inferred to be Double and the expressions cost + tip is an addition of two Double values, resulting in a Double value.

In your second (not working) example tip is declared to be Float therefore the expressions cost + tip is an error. The error message is not very informative. But the problem is that you are adding a Double to a Float and in a strongly statically typed language you will not have automatic type conversions like you had in C or Objective C.

You have to do either Float(cost) + tip or cost + Double(tip)