SE-0217 - The "Unwrap or Die" operator

[Erica_Sadun]

@masters3d

I thought about this too with something like panic() but this requires more logging of where the line crash happened (and others like calling func etc). otherwise the crashing line logged will always show up as where fatalError was called which wont be much help or be a sutable replacement for fatalError.

Introducing the Never-rhs variant of !! allows you to:

• Retain unsafe semantics with !! over ??. Limiting the rhs to Never ensures that any non-nil value will always have a non-returning outcome.
• Preserve the context information without extra compiler work (#file, #function, #line)
• Allow the rhs use of the universal-error scenarios discussed in this thread and proposal: Introducing Namespacing for Common Swift Error Scenarios - #22 by davedelong, also allowing the rhs extension to instances of the FatalReason, which has been designed for expansion to specific use scenarios:

wrappedURL !! fatalError(reason: .unconstructableURL)