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strictNullChecks limits what types can be accessed with indexed access types #21975
Description
TypeScript Version: 2.7.1-insiders.20180127
Search Terms: strictNullChecks mapped types property undefined generated types
Code
interface Foo {
bar?: {
baz: string;
}
}
type ShouldBeString = Foo['bar']['baz'];Expected behavior: Type ShouldBeString is a string type. This is useful especially for generated types where it isn't possible to write { baz: string } as a separate type.
Actual behavior: Accessing 'baz' errors with Property 'baz' does not exist on type '{ baz: string; } | undefined'.
Playground Link:
Make sure to toggle strictNullChecks on: https://www.typescriptlang.org/play/#src=interface%20Foo%20%7B%0D%0A%20%20%20%20bar%3F%3A%20%7B%0D%0A%20%20%20%20%20%20%20%20baz%3A%20string%3B%0D%0A%20%20%20%20%7D%0D%0A%7D%0D%0A%0D%0Atype%20ShouldBeString%20%3D%20Foo%5B'bar'%5D%5B'baz'%5D
Activity
mhegazy commentedon Feb 15, 2018
Duplicate of #16108, and #17370
nomcopter commentedon Feb 15, 2018
I'm don't think this is a duplicate Mohamed Hegazy (@mhegazy). This involves mapped types instead of the typeof operator.
nomcopter commentedon Feb 20, 2018
This issue may generalize more correctly to a feature request that the compiler should chose the "more useful" type when mapping through union types. For example the following example applies without
strictNullChecks:https://www.typescriptlang.org/play/index.html#src=interface%20Foo%20%7B%0D%0A%20%20%20%20bar%3A%20%7B%0D%0A%20%20%20%20%20%20%20%20baz%3A%20string%3B%0D%0A%20%20%20%20%7D%20%7C%20%7B%0D%0A%20%20%20%20%20%20%20%20qux%3A%20number%3B%0D%0A%20%20%20%20%7D%0D%0A%7D%0D%0A%0D%0Atype%20ShouldBeString%20%3D%20Foo%5B'bar'%5D%5B'baz'%5D
[-]strictNullChecks limits what types can be accessed with mapped types[/-][+]strictNullChecks limits what types can be accessed with indexed access typres[/+][-]strictNullChecks limits what types can be accessed with indexed access typres[/-][+]strictNullChecks limits what types can be accessed with indexed access types[/+]DanielRosenwasser commentedon Feb 20, 2018
See #14366 for the closer dupe.
nomcopter commentedon Feb 20, 2018
Would it be better to handle #14366 in the more general case by handling all union types? Should I update this issue?
typescript-bot commentedon Mar 7, 2018
Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.