OptionalToThrowingOverlay.swift

import Foundation

/*
Somewhere in Foundation

public protocol Foo {
	...
	public init<T>?(foo value: T) where T: Foo
	...
}
*/

extension Foo {
    init<T>(foo value: T) throws where T: Foo {
        guard let f = Self(foo: value) else {
            throw FooError.noap
        }
        self = f
    }
}