Swift 3 Decimal, NSDecimal and NSDecimalNumber

Question

I am trying to use NumberFormatter with Swift 3 Decimal, but I\'m confused as to how Decimal is really being implemented. The problem

Answer 1

I asked my question on the swift-users board and got a wonderful answer, check it out here: https://lists.swift.org/pipermail/swift-users/Week-of-Mon-20161219/004220.html

Text version of the response:

Swift 3 introduced the Decimal class, which at first I thought was supposed to 'replace' NSDecimalNumber in Swift, like Error is the new NSError, etc. However, upon further investigation, it's not clear to me that this is actually the case. It appears that Swift 3's Decimal is more just an NSDecimal, but with some bridging so it can use NSDecimalNumber's methods when needed. What I'm wondering is, should I be replacing NSDecimalNumber in my app with Decimal? Is Decimal the successor to NSDecimalNumber in Swift?

Decimal is actually a struct, not a class, and in fact it's just the Swift name for the NSDecimal struct in Objective-C. In Swift, functions like NSDecimalAdd are exposed as operators on Decimal and are used to satisfy the requirements of various numeric protocols like SignedNumber.

The end result is that Decimal is a lot like Int or Double—it's a value type which can be conveniently used to do all sorts of math. NSDecimalNumber, then, is equivalent to NSNumber.

Since my app is doing a lot of formatting, it would require much casting between Decimal and NSDecimalNumber, or adding of extensions to use, so I don't think it would be natural/convenient without many extensions. Is Swift planning to improve Decimal to be more usable with NumberFormatter, or other object-oriented number APIs? Hopefully I have given enough information to answer my question.

Objective-C APIs which use NSDecimalNumber should be bridged to Decimal, just as NSString is bridged to String. That bridging may not work for category methods, though; you could expose those to Swift by writing an extension on Decimal which casts self to NSDecimalNumber and then calls through to your Objective-C methods.

Similarly, you should be able to use Decimal with NumberFormatter by casting to NSDecimalNumber, just as you would cast Int or Double to NSNumber to use them with NumberFormatter.