An infix operator for collections that returns the wrapped value of the optional only if the collection is not empty.

Optional+Utilities.swift

import Foundation

infix operator ???

extension Optional where Wrapped: Collection {
    
    /// Performs a nil-coalescing operation, returning the wrapped value of an `Optional` instance
    /// only if the wrapped value is not empty, otherwise returns a default value.
    ///
    /// - Parameters:
    ///   - optional: An optional value.
    ///   - defaultValue: A value to use as a default.
    static func ??? (optional: Self, defaultValue: @autoclosure () -> Wrapped) -> Wrapped {
        if let wrappedValue = optional, !wrappedValue.isEmpty {
            return wrappedValue
        } else {
            return defaultValue()
        }
    }
    
}

defaultValue should be an @autoclosure () -> Self. If defaultValue is just a string literal, this isn’t a problem, but what if it’s an expensive function call? It should only be computed if needed, just like Optional’s ?? operator works

defaultValue should be an @autoclosure () -> Self. If defaultValue is just a string literal, this isn’t a problem, but what if it’s an expensive function call? It should only be computed if needed, just like Optional’s ?? operator works

Hey Emil 👋

I actually did try to do that initially, as it is done with ?? like you said, but it results in this error:
Member operator '???' of protocol 'Collection' must have at least one argument of type 'Self'

But I agree that it would be better using a closure. Any ideas?

Oh yeah, you'll have to put the extension on Optional where Wrapped: Collection so the left hand side can be of type Self:

import Foundation

infix operator ???

extension Optional where Wrapped: Collection {
    
    /// Performs a nil-coalescing operation, returning the wrapped value of an `Optional` instance
    /// only if the wrapped value is not empty, otherwise returns a default value.
    ///
    /// - Parameters:
    ///   - optional: An optional value.
    ///   - defaultValue: A value to use as a default.
    static func ??? (optional: Self, defaultValue: @autoclosure () -> Wrapped) -> Wrapped {
        if let wrappedValue = optional, !wrappedValue.isEmpty {
            return wrappedValue
        } else {
            return defaultValue()
        }
    }
    
}

Great idea! I updated it, thanks 👍