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Initializing let variables and exhaustiveness checking #22470

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#32695
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Initializing let variables and exhaustiveness checking#22470
#32695
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@rauschma
Axel Rauschmayer (rauschma)
opened on Mar 11, 2018
let tagName;
switch (kind) {
  case ListKind.Ordered:
    tagName = 'ol';
    break;
  case ListKind.Unordered:
    tagName = 'ul';
    break;
  default:
    assertNever(kind);
}
  • The inferred type of tagName is string|undefined, but should be string, AFAICT.
  • Similarly: If I give tagName the type string, I get the error: “Variable 'tagName' is used before being assigned”.

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  1. ajafff commented on Mar 11, 2018

    @ajafff
    Klaus Meinhardt (ajafff)
    on Mar 11, 2018
    Contributor

    Control flow analysis does not know that assertNever never returns. You need to return or throw assertNever(kind); to end the control flow.

  2. rauschma commented on Mar 11, 2018

    @rauschma
    Axel Rauschmayer (rauschma)
    on Mar 11, 2018
    Author

    That makes sense! Thanks!

  3. Axel Rauschmayer (rauschma)
    closed this as completedon Mar 11, 2018
  4. Ryan Cavanaugh (RyanCavanaugh)
    added
    DuplicateAn existing issue was already created
    on Mar 12, 2018
  5. microsoft
    locked and limited conversation to collaborators on Jul 25, 2018
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