Why can't Int.init() take an optional StringProtocol?

[Nevin]

@Lantua

Feels like suffix ? was the closest one we've got, not that there's much room for variations.

As I recall, in the last thread about it (Unwrapped Arguments for Functions), there was broad agreement that postfix-? was the right spelling.

Prior discussions had bogged down in debating evaluation order and short-circuiting, but then Rob Mayoff observed that we have already answered exactly those questions for try, and it would make sense to match the behaviors:

@mayoff

There is already a construct in the language similar to the one you propose: a throwing expression. We should look at how it interacts with the evaluation rules.

For example, here's an expression using your proposed syntax:

f(a, maybe0()?, b, maybe1()?, c)

and here is the analogous expression with throwing subexpressions:

try? f(a, try mightThrow0(), b, try mightThrow1(), c)

Note that any of the identifiers in either expression could refer to a computed property or in general could be replaced by a function call or an arbitrarily complex subexpression.

[...]

I would prefer both expressions to follow the same rules, and we can't change the rules for the throwing expression without breaking source compatibility.

Since throwing in argument position will short-circuit and prevent evaluation of subsequent arguments, it follows that a nil argument with postfix-? should do the same.

If that is something we want in the language, I believe the spelling and behavior are essentially nailed down. It’s just a matter of making it happen.