Documentation for exception thrown within `when` expression

[romglusker]

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Type of issue

Missing information

Description

I could not find good documentation on the expected behavior if an exception is thrown within the when expression. I wanted to confirm whether any additional exception handling was necessary in this use case.

Based on a quick test, it appears that the exception is suppressed, and the associated exception handler does not execute. Can the behavior be documented?

Page URL

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/when

Content source URL

https://github.com/dotnet/docs/blob/main/docs/csharp/language-reference/keywords/when.md

Document Version Independent Id

15502bbc-5355-2add-0fa8-ae31dc01c122

Article author

@BillWagner

Metadata

• ID: 6ef10b29-fbf8-5af9-8f8b-a694a1416e33
• Service: dotnet-csharp
• Sub-service: lang-reference

[adamsitnik]

@janvorli who would be the best person to improve the docs for exception handling?

[BillWagner]

Adding @jcouv and @333fred

/cc @jskeet

I looked through the latest standard:

• Try statement
• Throw statement

Neither specify behavior when evaluating an exception_filter throws an exception.

One requirement can be teased out: The language in the standard says that the catch clauses matches "when the exception_filter evalutes to true". Throwing an exception should mean the catch clause isn't execute.

The standard does have rules for the behavior when an exception is propagated from a catch clause, so the behavior when an exception filter thows an exception should be part of the standard.

If you both agree, I'll move this to the csharpstandard repo.

[jskeet]

Yes, we should definitely document this.

[BillWagner]

@jskeet I propose adding this to the C# 8 milestone.

[jskeet]

Yup, works for me.