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Weird uninitialized variable error for destructured members of type parameter constrained to homomorphic mapped type where member is declared optional #20994
Description
Found in Formik by Wesley Wigham (@weswigham) who patiently worked with me to find the minimal repro.
Run the following with strictNullChecks
interface Options {
a?: number | object;
b: () => void;
}
class C<T extends Options> {
foo!: { [P in keyof T]: T[P] }
method() {
let { a, b } = this.foo;
!(a && b)
a
// TypeScript issues an error on 'a' above:
// Variable 'a' is used before being assigned.'
}
}
Activity
rozzzly commentedon Jan 4, 2018
Daniel Rosenwasser (@DanielRosenwasser)
Is the
!:some new/obscure syntax I'm not aware of? Or just a typo?ahejlsberg commentedon Jan 4, 2018
Patrick Lienau (@rozzzly) See #20166.
sandersn commentedon Jan 19, 2018
Should be fixed #20995