Repository navigation
Unable to add numeric types that are not simply 'number' #17069
Description
I'm trying to rewrite the signature of sum from core.ts in our compiler (see #16823), but I'm getting this error:
export function sum<T extends Record<K, number>, K extends string>(array: T[], prop: K): number {
let result = 0;
for (const v of array) {
result += v[prop];
// ~~~~~~~~~~~~~~~~~
// Operator '+=' cannot be applied to types 'number' and 'T[K]'.
}
return result;
}Note that I can't declare sum as
export function sum<K extends string>(array: Record<K, number>[], prop: K): numberbecause then TypeScript would infer all of the properties in each element for K. So I do need another type argument T for the indirection.
For a simpler repro:
function foo<T extends number>(x: T) {
return 0 + x;
// ~~~~~
// Operator '+' cannot be applied to types '0' and 'T'.
}Related is #15645.
Activity
[-]Unable to add types constrained to 'number'[/-][+]Unable to add types that are not simply 'number'[/+][-]Unable to add types that are not simply 'number'[/-][+]Unable to add numeric types that are not simply 'number'[/+]Fix #17069 and #15371
sandersn commentedon Aug 17, 2017
Fix is up at #17870
sandersn commentedon Aug 17, 2017
Note that #17404 fixed the simpler repro; #17870 fixes the original issue with a type parameter indexed by another type parameter.
Fix #17069 and #15371
sandersn commentedon Aug 18, 2017
The previous PR got merged by mistake and is now reverted; #17912 is the PR with the fix now.