Implement constructor check type guard #32256
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austincummings
commented
Jul 4, 2019
| bar.prop1; // string | ||
| bar.prop2; // number | ||
| } | ||
| if (bar.constructor === Foo) { |
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As far as I can tell, this should always be false. Right now the type get's narrowed to Bar in the if, is this right? Or should it narrow just to Foo?
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Shouldn't it narrow to never inside the if since Bar | boolean can never satisfy the condition?
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@fatcerberus That's a good point. I didn't think about narrowing to never. Seems like the thing to do. I'll change this. Thanks.
austincummings
commented
Jul 4, 2019
src/compiler/checker.ts
Outdated
| @@ -17000,6 +17006,13 @@ namespace ts { | |||
| return narrowType(type, expr.right, assumeTrue); | |||
| } | |||
| return type; | |||
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| function isConstructorAccessExpression(expr: Expression): expr is AccessExpression { | |||
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Is there somewhere else I should put this or is this ok?
austincummings
commented
Jul 4, 2019
src/compiler/checker.ts
Outdated
| return ( | ||
| isPropertyAccessEntityNameExpression(expr) && idText(expr.name) === "constructor" | ||
| || isElementAccessExpression(expr) && isStringLiteralLike(expr.argumentExpression) && expr.argumentExpression.text === "constructor" | ||
| ); |
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Not sure on the formatting of this...
|
Closing to reopen a fresh PR with much more detail. |
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Fixes #23274
This builds on work done by @Kingwl in PR #23622 to add a new type guard checking for the
instance.constructor === Constructorsyntactic pattern to narrow the type ofinstance.I'm making this a draft PR as there's a couple things I need some guidance on.
Thanks!