[Pitch] Non-nil assignment and shorthand nil checks

Evolution Pitches
12

This pitch is good but too constrained. It needs to apply to anything that is a throwing property wrapper. Neither Optional nor Result have been converted to be so, but they need to be, as that's what they represent.

As it is, what @tera said is necessary:

public extension ThrowingPropertyWrapper {
  /// Assign only non-throwing values.
  static func =? (self0: inout Self, self1: Self) {
    if .success(catching: try self1.wrappedValue) {
      self0 = self1
    }
  }

  /// Assign only non-throwing values.
  static func =? (wrappedValue: inout WrappedValue, self: Self) {
    try? wrappedValue = self.wrappedValue
  }
}

But @ramzesenok's proposed syntax is what actually should be used. ? should consistently mean "or do nothin' " when it comes afterwards. E.g.

var result = Result { "🪕" }
var success = "🎻"
result =? .init { success }
success =? result

should be

@Result var result = "🪕"
var success = "🎻"
result = .init { success }?
success = result?

I can understand that reading, but that's already what = does without ? appended. ? should mean something different.