Nullable reference types in F# #44047
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@T-Gro PTAL - I didn't want to copypaste your whole blog post to one place so tried to distribute the information among the various related docs... If you think I over- or under-copied something, let me know, will update this accordingly - the null-related information shouldn't be overwhelming but should be exhaustive. |
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A checklist of things I expect to see in the docs (will tick the ones I identified while reviewing):
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psfinaki
requested review from
BillWagner,
KathleenDollard and
a team
as code owners
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@T-Gro thanks for the checklist, all valid points, I think I have addressed the missing parts. |
| let checkNonNull argName (arg: obj) = | ||
| match arg with | ||
| // nullness warning: the type 'obj' does not support 'null' | ||
| | null -> nullArg argName |
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The if-else branches show identical code here.
Motivating example could e.g. be with a conditional not null constraint, or perharps for exposing a part of an public API.
Even the MaybeNull alias/wrapper could be used.
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Well, the idea was that the compiler directive makes the compiler produce a warning. We can have something more useful here - I added an example but not sure it counts really.
| else () | ||
| ``` | ||
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| To address the warnings, you could explicitly specify `null` as a possible argument value: |
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This needs rework based on how the first example is redone.
Right now, it shows the wrong incentive.
If e.g. the first example shows a warning for (string|null).Length, that this example should show how to handle it.
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I removed and reworked the text, take a look if it's more consistent and helpful now.
| Here is an example of the valid usage of the syntax: | ||
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| ```fsharp | ||
| let processStream (stream: System.IO.StreamReader) = |
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The example has some value, but it is unrelated to the text:
The text speaks about API boundaries, but here the processLine is private to the function, so not exposed to the outside world...
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Yeah, fair point. I updated the example but still don't like it too much... it might help to add something from the real world, like implementing some tiny .NET interface with nulls - would you have something from the top of your head?
| | null -> ... | ||
| ``` | ||
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| Note that the extra null related capabilities were added to the language for the interoperability purposes. Using `| null` within F# code is not considered idiomatic for denoting missing information - for that purpose, use options (as described above). Read more about null-related [conventions](../../style-guide/conventions.md#nulls-and-default-values) in the style guide. |
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This should be a lot more targeted.
- Make sure this is speaking about type modelling (|null can be used internally, in pattern matching, for function arguments,..), nothing else
- Make sure this is speaking about signalling a possible absence of value, and is not enforced by interop API boundaries
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I reformulated the sentence a bit - don't want to elaborate too much since this is what conventions page is for...
Closes dotnet/fsharp#17829
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