Type conversion

Sometimes you’ll have data in one format and need to convert it to another. The naïve way to attempt this would be like so:

var integer: Int = 100 var decimal: Double = 12.5 integer = decimal

Swift will complain if you try to do this and spit out an error on the third line:

Cannot assign value of type 'Double' to type 'Int'

Some programming languages aren’t as strict and will perform conversions like this automatically. Experience shows this kind of automatic conversion is the source of software bugs and often hurts performance. Swift disallows you from assigning a value of one type to another and avoids these issues.

Remember, computers rely on us programmers to tell them what to do. In Swift,

that includes being explicit about type conversions. If you want the conversion to happen, you have to say so!

Instead of simply assigning, you need to explicitly say that you want to convert the type. You do it like so:

var integer: Int = 100 var decimal: Double = 12.5 integer = Int(decimal)

The assignment on the third line now tells Swift unequivocally that you want to convert from the original type, Double, to the new type, Int.

Note: In this case, assigning the decimal value to the integer results in a loss of precision: The integer variable ends up with the value 12 instead of 12.5.

This is why it’s important to be explicit. Swift wants to make sure you know what you’re doing and that you may end up losing data by performing the type conversion.