Why does NumberFormatter's string(from:) return an optional?

Question

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Why does the NumberFormatter function func string(from number: NSNumber) -> String? return a String? rat

Answer 1

Just for fun: Here is a (constructed, not real-world) example where string(from:) actually returns nil:

let num = NSNumber(bytes: UnsafeRawPointer(bitPattern: 1)!, objCType: "v")
print(num) // <>

let fmt = NumberFormatter()
fmt.numberStyle = .decimal
let str = fmt.string(from: num)

print(str as Any) // nil

The reason is that this num does not represent a number: It is created using the NSValue (from which its inherits) initializer init(bytes:objCType:) with a value representing void. ("v" is the type encoding for void, the pointer value is irrelevant.)