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Switch on typeof for keyof type loses information #27181
Description
TypeScript Version: master 83fe1ea
Search Terms: switch typeof keyof intersection
Code
function keyofNarrowing<S extends { [K in keyof S]: string }>(k: keyof S) {
switch (typeof k) {
case 'number': k; return; // k has type number, should be keyof S & number
case 'symbol': k; return; // k has type number, should be keyof S & symbol
case 'string': k; return; // k has type number, should be keyof S & string
}
}Expected behavior:
The value k should narrow to an intersection type to retain keyof type.
Actual behavior:
The value k narrows to a primitive.
Playground Link: N/A (Playground not on this version).
Activity
ahejlsberg commentedon Sep 18, 2018
This one is fixed by #27157.
jack-williams commentedon Sep 18, 2018
Great, I'll remove the fix I put in for #27182 (but will keep the tests). This will mean #27182 is blocked on #27157 but that seems ok I think.