A conditional operator literal string type problem

[BirdLeeSCUT]

TypeScript Version: 2.1.5

There is a conditional operator literal string type problem, ts cannot resolve true ? "a" : "b" as a type, which may call some errors.

for example:

type a_or_b = "a" | "b" ;
let v1 = (true ? "a" : "b");
let v2: a_or_b;
v2 = v1; // ERROR

Expected behavior:
expect no error.

Actual behavior:
but it comes up with an error as follow:
TS2322

I know a solution to refrain this error is changing the line 2 to be let v1: any = (true ? "a" : "b"); or let v1: a_or_b = (true ? "a" : "b"); , but this procedure seem to should be needless.

[krryan]

Try const v1 = (true ? "a" : "b");. Since you are using let you are allowing v1 to be reassigned and the compiler assumes you want it to accept the wider range of values (string), but with const it can be narrower.

(What actually surprises me here is that it infers the type of const v1 as "a" | "b" rather than "a" which is clearly the only thing it can actually be; I made a separate bug for that)

[BirdLeeSCUT]

@krryan Thanks, it works well!