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function needsToNarrowTheType<First extends { foo: string }, Second extends { bar: string }, SubFirst extends First, SubFirstMore extends First & {other: string}>(thing: First | SubFirst | SubFirstMore | Second) {
if (hasAFoo(thing)) {
console.log(thing.foo);
}
else {
// I would expect this to work because the type should be narrowed in this branch to `Second`
console.log(thing.bar); // Error: Property 'bar' does not exist on type 'First | Second'.
}
function hasAFoo(value: First | Second): value is First {
return "foo" in value;
}
}
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