4 ms·

The state machine example is a good one. It's a textbook case of unreachable code. The null-checking example is not good. If the external API returns a null

The state machine example is a good one. It's a textbook case of unreachable code. The null-checking example is not good. If the external API returns a null where you don't expect one, UnreachableException will be thrown. It doesn't matter if the documentation says it will never be null; clearly the code isn't unreachable. All you need to reach it is bad data! (InvalidDataException would be a better choice, though arguably not an ideal one.) If you can write a unit test that makes your code throw UnreachableException, you almost certainly should be throwing a different exception.

WirelessGigabit 4y ago
Invalid date means you got a value that’s not a valid date which is different than falling into an impossible state.
- AlfeG 4y ago
  Invalid Data, not date
  - necovek 4y ago
    I would guess they were spell-checker-corrected, and meant "data" both times: the sentence makes sense with either, though "data" is obviously what makes it make sense in this context :)
ad133 4y ago
This was my initial thought as well, but from the text I gather there is a flow like this: [Input Data, maybe null] -> Validate field is not null -> Call this method with the assertion. This is a small bug-bear for me with nullable types and I wish there was a better way to do it, but many languages allow you to smart-cast away nulls, but only within the local scope. If you want to pass a struct-type around which has nullable fields, but you have already checked for non-null (like this one) you need to convert to a different struct-type, which doesn't have the nullability on its fields. I can't think of a good way round this - as you say with the unit test remark, there is nothing to stop another piece of code calling this method with nulls.
- piaste 4y ago
  > If you want to pass a struct-type around which has nullable fields, but you have already checked for non-null (like this one) you need to convert to a different struct-type, which doesn't have the nullability on its fields. Which is exactly what IMO the author should have done. It's actually a reasonable use-case for inheritance: #nullable enable record SlackEvent ( int EventId , string Content , string? TeamId ); record TeamSlackEvent ( int EventId , string Content , string TeamId ) : SlackEvent ( EventId : EventId , Content : Content , TeamId : TeamId );
gwbas1c 4y ago
> If you can write a unit test that makes your code throw UnreachableException, you almost certainly should be throwing a different exception. ArgumentNullException, InvalidOperationException... There's plenty that have been around since the beginning. What's more important, that I didn't see in the first two examples, are useful error messages.
- aloisdg 4y ago
  `ArgumentNullException` was my first idea too. I would and did use it for this kind of purpose.

WirelessGigabit 4y ago

Invalid date means you got a value that’s not a valid date which is different than falling into an impossible state.

AlfeG 4y ago
Invalid Data, not date
- necovek 4y ago
  I would guess they were spell-checker-corrected, and meant "data" both times: the sentence makes sense with either, though "data" is obviously what makes it make sense in this context :)

ad133 4y ago

This was my initial thought as well, but from the text I gather there is a flow like this: [Input Data, maybe null] -> Validate field is not null -> Call this method with the assertion. This is a small bug-bear for me with nullable types and I wish there was a better way to do it, but many languages allow you to smart-cast away nulls, but only within the local scope. If you want to pass a struct-type around which has nullable fields, but you have already checked for non-null (like this one) you need to convert to a different struct-type, which doesn't have the nullability on its fields. I can't think of a good way round this - as you say with the unit test remark, there is nothing to stop another piece of code calling this method with nulls.

piaste 4y ago
> If you want to pass a struct-type around which has nullable fields, but you have already checked for non-null (like this one) you need to convert to a different struct-type, which doesn't have the nullability on its fields. Which is exactly what IMO the author should have done. It's actually a reasonable use-case for inheritance: #nullable enable record SlackEvent ( int EventId , string Content , string? TeamId ); record TeamSlackEvent ( int EventId , string Content , string TeamId ) : SlackEvent ( EventId : EventId , Content : Content , TeamId : TeamId );

gwbas1c 4y ago

> If you can write a unit test that makes your code throw UnreachableException, you almost certainly should be throwing a different exception. ArgumentNullException, InvalidOperationException... There's plenty that have been around since the beginning. What's more important, that I didn't see in the first two examples, are useful error messages.

aloisdg 4y ago
`ArgumentNullException` was my first idea too. I would and did use it for this kind of purpose.