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Can't use keyof index for indexing intersection of Partial<T> and another type in generic class<T>. #22286
Description
Bug
I'm trying to use an object's key to index an intersection into a partial of an object and another object, but I'm getting an error.
Note: this error only shows up in a generic class. Using plain types I was not able to replicate it.
TypeScript Version:
2.7.1-insiders.20180127 (playground)
2.3.1 (visual studio tools)
2.7.2 (command line)
Search Terms:
Keyof, intersection, union, Partial, index, merge.
Code
interface Rum {
"ho hum": string;
}
interface Color {
"blue": number;
}
class Thingy<T> {
mything: Rum & Partial<T>;
log(param: keyof T) {
console.log(this.mything[param]); //ERROR!
}
}Expected behavior:
No errors.
Actual behavior:
test.ts(13,25): error TS2536: Type 'keyof T' cannot be used to index type 'Rum & Partial'.
Activity
mhegazy commentedon Mar 2, 2018
Should be fixed by #22300
Griffork commentedon Mar 3, 2018
Mohamed Hegazy (@mhegazy) does this mean that the best typing I'm going to get is
this.mything[param]: string | number?mhegazy commentedon Mar 3, 2018
it is actually
(Rum & Partial<T>)[keyof T], which is generic, and not assignable tostring | number, sinceTcan have additional properties when it is instantiated.