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Strange type narrowing with Discriminated union types #9254
Description
TypeScript Version:
nightly (1.9.0-dev.20160619-1.0)
Expected behavior:
Type of shape should be never or Shape so that we can still access type to throw an Error.
throw new Error('Unknown type. Type: ' + shape.type);Actual behavior:
Type of shape is { type: 'rectangle'; width: number; height: number }.
Activity
ahejlsberg commentedon Jun 19, 2016
Duplicate of #9246. This is working as intended because of #8548, but it is obviously causing some confusion.
yortus commentedon Jun 20, 2016
Anders Hejlsberg (@ahejlsberg) how do the conditions of #8548 come up with this example? The control flow type is (or should be?) narrowed to
neverafter the two type guards in theif/else ifblock. But then there is no third type guard that conflicts with that narrowed type, so why should #8548 apply?ahejlsberg commentedon Aug 3, 2016
Fixed in #10118.