Typescript 2 - throw'ing in ternary/conditional operator expression

Question

I try to compile:

const value = "20"
const x : string | never = "10" === value ? throw Error("bad things") : "hello"

... and get an error on throw - expression expected. I can resolve this using an inline method invoked in place, but that does not look nice. ((() => {throw Error("bad things"})())

Why is not OK to throw in a branch of the ternary operator? Or is there another syntax that works, perhaps compile options I'm missing?

Throw does not seem to work without curly brackets in the function body either, in the work-around, ((() => throw Error("bad things")()).

Answer 1

It's a syntactic quirk of the language.

The statement throw ex can be regarded as an expression that has the type never, because never is the type of functions that don't return, which is exactly what happens when you throw. In many languages that have a bottom type (the technical term for what never is -- it's not merely an "odd keyword").

The statement throw ex is different from, for example, the statement for (let x of ...) because the latter cannot be understood to return anything, whereas throw ex can be understood to return never.