`abstract class` should be usable in expressions

🔍 Search Terms

abstract, class, expression

✅ Viability Checklist

• 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 isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
• This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

⭐ Suggestion

function myMixin(Base: typeof Object) {
  return abstract class Mixed extends Base {};
}

📃 Motivating Example

Preferable to:

function myMixin(Base: typeof Object) {
  abstract class Mixed extends Base {}
  return Mixed;
}

💻 Use Cases

1. What do you want to use this for?
   Same uses as without
2. What shortcomings exist with current approaches?
   Slight additional verbosity
3. What workarounds are you using in the meantime?
   Slight additional verbosity

提案されたmixinの例と、その動機となる比較から始めて、受け入れられる式の形式とその型チェックの動作を定義します。次に、クラス宣言とクラス式に対するコンパイラのエントリポイントを追跡し、最後に、例が型チェックを通過し、実行時の出力に変更がないことを確認します。