`abstract class` should be usable in expressions

[stwlam]

🔍 Search Terms

abstract, class, expression

✅ Viability Checklist

• [X] This wouldn't be a breaking change in existing TypeScript/JavaScript code
• [X] This wouldn't change the runtime behavior of existing JavaScript code
• [X] This could be implemented without emitting different JS based on the types of the expressions
• [X] This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• [X] This isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
• [X] 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

[whzx5byb]

https://github.com/microsoft/TypeScript/issues/4578 was declined, but since it's 9 years, maybe it's time to revisit it.

[stwlam]

4578 was declined, but since it's 9 years, maybe it's time to revisit it.

Interesting!

[stwlam]

Some additional issue corralling: it looks like the reporter of #32122 was basically running into the same problem, though the errors they pasted aren't the same.