In a union, types with index signatures should contribute types to all properties #21141
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mhegazy
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RyanCavanaugh
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@sandersn let's give it a try |
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This means that in a union like this:
```ts
type T = { foo: number } | { [s: string]: string }
```
`foo` is now a property of `T` with type `number | string`. Previously
it was not.
Two points of interest:
1. A readonly index signature makes the resulting union property readonly.
2. A numeric index signature only contributes number-named properties.
Fixes #21141
This was referenced Jul 2, 2018
sandersn
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* Index signatures contribute properties to unions
This means that in a union like this:
```ts
type T = { foo: number } | { [s: string]: string }
```
`foo` is now a property of `T` with type `number | string`. Previously
it was not.
Two points of interest:
1. A readonly index signature makes the resulting union property readonly.
2. A numeric index signature only contributes number-named properties.
Fixes #21141
* Correctly handle numeric and symbol property names
1. Symbol-named properties don't contribute to unions.
2. Number-named properties should use the numeric index signature type,
if present, and fall back to the string index signature type, not the
other way round.
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Currently, putting a type with nothing but a string index signature in a union prevents all properties from being accessible. Instead, the type should contribute its index type to all properties:
Currently,
fooandbazare not found onu. But they should be present, and have types{ bar: true } | stringandtrue | stringrespectively.The text was updated successfully, but these errors were encountered: