Decimal to Double conversion in Swift 3

NSDecimalNumber and Decimal are bridged

The Swift overlay to the Foundation framework provides the Decimal structure, which bridges to the NSDecimalNumber class. The Decimal value type offers the same functionality as the NSDecimalNumber reference type, and the two can be used interchangeably in Swift code that interacts with Objective-C APIs. This behavior is similar to how Swift bridges standard string, numeric, and collection types to their corresponding Foundation classes. Apple Docs

but as with some other bridged types certain elements are missing.

To regain the functionality you could write an extension:

extension Decimal {    var doubleValue:Double {        return NSDecimalNumber(decimal:self).doubleValue    }}// implementationlet d = Decimal(floatLiteral: 10.65)d.doubleValue

Another solution that works in Swift 3 is to cast the Decimal to NSNumber and create the Double from that.

let someDouble = Double(someDecimal as NSNumber)

As of Swift 4.2 you need:

let someDouble = Double(truncating: someDecimal as NSNumber)

Solution that works in Swift 4

let double = 3.14let decimal = Decimal(double)let doubleFromDecimal = NSDecimalNumber(decimal: decimal).doubleValueprint(doubleFromDecimal)