Swift - How to convert String to Double

Question

I'm trying to write a BMI program in swift language. And I got this problem: how to convert a String to a Double?

In Objective-C, I can do like this:

double myDouble = [myString doubleValue];

But how can I achieve this in Swift language?

Answer 1

Swift 2 Update There are new failable initializers that allow you to do this in more idiomatic and safe way (as many answers have noted, NSString's double value is not very safe because it returns 0 for non number values. This means that the doubleValue of "foo" and "0" are the same.)

let myDouble = Double(myString)

This returns an optional, so in cases like passing in "foo" where doubleValue would have returned 0, the failable intializer will return nil. You can use a guard, if-let, or map to handle the Optional<Double>

Original Post: You don't need to use the NSString constructor like the accepted answer proposes. You can simply bridge it like this:

(swiftString as NSString).doubleValue