51 lines
1.5 KiB
Markdown
51 lines
1.5 KiB
Markdown
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# null-conditional await
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* [x] Proposed
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* [ ] Prototype: None
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* [ ] Implementation: None
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* [ ] Specification: Started, below
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## Summary
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[summary]: #summary
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Support an expression of the form `await? e`, which awaits e if it is non-null, otherwise it results in `null`.
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## Motivation
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[motivation]: #motivation
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This is a common coding pattern, and this feature would have nice synergy with the existing null-propagating and null-coalescing operators.
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## Detailed design
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[design]: #detailed-design
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We add a new form of the *await_expression*:
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``` antlr
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await_expression
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: 'await' '?' unary_expression
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;
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```
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The null-conditional `await` operator awaits its operand only if that operand is non-null. Otherwise the result of applying the operator is null.
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The type of the result is computed using the [rules for the null-conditional operator](https://github.com/dotnet/csharplang/blob/master/spec/expressions.md#null-conditional-operator).
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## Drawbacks
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[drawbacks]: #drawbacks
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As with any language feature, we must question whether the additional complexity to the language is repaid in the additional clarity offered to the body of C# programs that would benefit from the feature.
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## Alternatives
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[alternatives]: #alternatives
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Although it requires some boilerplate code, uses of this operator can often be replaced by an expression something like `(e == null) ? null : await e` or a statement like `if (e != null) await e`.
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## Unresolved questions
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[unresolved]: #unresolved-questions
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- [ ] Requires LDM review
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## Design meetings
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None.
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