flight-school/guide-to-swift-numbers-sample-code

Xcode Playground Sample Code for the Flight School Guide to Swift Numbers

guide-to-swift-numbers-sample-code's Issues

Remove faulty float literal initialization from Money type

The book is fantastic as usual but it contains a classic mistake in the Money type: The ExpressibleByFloatLiteral fallacy :)

This undos all of the good intentions of having exact values in the type.

let m = Money<USD>(floatLiteral: 0.14)
m.amount

Here m.amount is now 0.14000000000000002048 which is clearly not exact anymore.

The reason I guess is that the literal is always first converted to a Float, and only then to a Decimal.

If you want any literal initialization, you need to use the String initializer because Decimal(string: "0.14") is indeed 0.14 now.

See my related Swift post
https://forums.swift.org/t/exact-nsdecimalnumber-via-literal/12834

and tracking bugs:
https://bugs.swift.org/browse/SR-3317
https://bugs.swift.org/browse/SR-920

Sure one can argue "but for the purpose of this book…" but that's not what the Flight School books are about. They are precise, and that's what makes them so darn good.