In a loop, multiple errors are sometimes reported on the same location, but with slightly different types.
@ahejlsberg Any idea what's going on?
TypeScript Version:
nightly (1.9.0-dev.20160430)
Code
function test<U>(xs: U[], combine: (a: U, b: U) => U) {
let hasValue = false;
let value: U | undefined;
for (const x of xs) {
if (hasValue) {
value = combine(value, x);
} else {
hasValue = true;
value = x;
}
}
}Expected behavior:
Only one error should be reported:
value = combine(value, x);
~~~~~ Argument of type 'U | undefined' is not assignable to parameter of type 'U'.
Type 'undefined' is not assignable to type 'U'.
By adding an exclamation mark to that line (value = combine(value!, x);), no error should be reported.
Actual behavior:
Two errors are reported:
value = combine(value, x);
~~~~~ Argument of type 'U | undefined' is not assignable to parameter of type 'U'.
Type 'undefined' is not assignable to type 'U'.
~~~~~ Argument of type 'undefined' is not assignable to parameter of type 'U'.
Adding an exclamation mark gives:
value = combine(value!, x);
~~~~~~ Argument of type 'nothing' is not assignable to parameter of type 'U'.
In a loop, multiple errors are sometimes reported on the same location, but with slightly different types.
@ahejlsberg Any idea what's going on?
TypeScript Version:
nightly (1.9.0-dev.20160430)
Code
Expected behavior:
Only one error should be reported:
By adding an exclamation mark to that line (
value = combine(value!, x);), no error should be reported.Actual behavior:
Two errors are reported:
Adding an exclamation mark gives: