No warning when using unary +/- operators on functions and objects?

TypeScript Version: 2.6.1

Code

let func = () => "func";
+func; // no error
-func; // no error

let obj = { foo: "bar" };
+obj; // no error
-obj; // no error

Expected behavior:
Unary + or - is only applicable to a number or maybe a string. I would expect the lines listed as // no error to be errors.

Actual behavior:
Unary + and - never generates a warning no matter what crazy stuff I try to apply it to.

I was made aware of this behavior by a recent Stack Overflow question. I see from #7019 that unary + and - on strings is supported, and I guess I can understand that as a way to parse a string into a number (for +, anyway. Is - really used like this in practice?). But functions? objects? Seems more likely to be an error than intentional to me. Thoughts?

TypeScript 2.6.1 の例を再現し、関数、オブジェクト、文字列に対する単項 + と - の診断を比較します。既存の単項演算子の型チェック動作を確認します。完了条件は、意図した無効なオペランドでエラーが発生し、サポートされている文字列の動作が意図的なものとして維持され、テストでカバーされていることです。