Additive inverse of number literals

Search Terms

Using unary minus on variable that is of number-literal type. Negative number literals.

Suggestion

This is a specific case of #26382. My proposal is simply that if we apply unary minus on an expression whose type is a union of number literal types, the result should be a union of their additive inverses:

declare var a: 1 | 2 | 3;
const b = -a; // should be -1 | -2 | -3

Furthermore we could add a unary minus type operator:

-(42) === -42
-(A | B) === -A | -B
-number === number
-(not number) // error

Both should be very easy and uncontroversial to implement.

Use Cases

function compare(a: C, b: C): -1 | 0 | 1;

function reverseCompare(a: C, b: C): -1 | 0 | 1
{
  return -compare(a, b); // shouldn't throw an error
}

The type operator would be just for sake of completeness

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

まず issue #26382 の関連提案と、数値リテラルのユニオンに対する単項マイナスの型チェック動作を確認します。完了条件は、例から -1 | -2 | -3 が推論され、reverseCompare が受け入れられる一方で、無効な非数値オペランドは引き続きエラーになることです。issue ではソースファイルやテストは指定されていません。