Only assign new values when the right operand is not nil

It’s sometimes useful to create custom operators to avoid boilerplate code. For example in the following code, we check if a variable is not nil before assigning it to our object:

if let basedOn = basedOn {
    story.basedOn = basedOn
}

It would be much better if we could simplify and have this instead:

story.basedOn ?= basedOn

To do that in Swift, we can create an “Optional Assignment” custom operator, as short as ?= here, with a few lines of code:

import Foundation
precedencegroup OptionalAssignment {
associativity: right
}
infix operator ?=: OptionalAssignment
public func ?= <T>(variable: inout T, value: T?) {
if let unwrapped = unwrap(any: value) ?? nil {
variable = unwrapped
}
}
public func unwrap<T: Any>(any: T) -> T? {
let mirror = Mirror(reflecting: any)
guard mirror.displayStyle == .optional else { return any }
guard let child = mirror.children.first else { return nil }
return unwrap(any: child.value) as? T
}
view raw OptionalAssignment.swift hosted with ❤ by GitHub

Leave a Reply

Your email address will not be published. Required fields are marked *