Allow concatenated strings to be cast as const type

Suggestion

🔍 Search Terms

Concatenated strings const type

✅ Viability 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, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

Allow as const cast to be applied to concatenated string literals like so:

// s0 would be 'ab'
const s0 = ('a' + 'b') as const;

https://www.typescriptlang.org/play?#code/FAehAIGcAZwdwPYFcA2ATcAjApuA5AIaZ7ADGCAdpAC5SwC84AFIXuANT7ECU4Bk4clWoBuYKAiQAjOACWAwsTKUaUGY0Vt+glaKA

📃 Motivating Example

It's convenient to split a long string into multiple concatenated lines to enhance code readability, so as const cast should work for it as well.

💻 Use Cases

Currently only a single string is allowed to be cast to its literal type. So as a workaround you just sacrifice code readability and make multiple strings into one:

'a' + 'b' => 'ab'

Issue にリンクされている連結リテラルの例と TypeScript の設計目標から始めます。as const が現在、単一の文字列リテラルと連結をどのように扱っているかを確認し、生成される JavaScript を維持しながら、完了を定義するコンパイラテストと型チェックの動作を特定します。