Description
🔍 Search Terms
Hi all,
is there any plan to allow implicit types when a class is anyways implementing an interface, function types are well defined, but still need to redeclare function types on the class:
thanks in advance
✅ 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
It would be cleaner if developer is not forced to redeclare function types when implementing functions coming from an interface
📃 Motivating Example
I'd like to propose an enhancement that could significantly reduce code duplication and improve developer experience.
Currently, when a class implements an interface, we're required to redeclare method types even though they're already defined in the interface:
interface UserService {
getUser(id: string): Promise;
updateUser(user: User): Promise;
}
class UserServiceImpl implements UserService {
// We have to repeat types even though they're defined in the interface
async getUser(id: string): Promise { ... }
async updateUser(user: User): Promise { ... }
}
Since the class explicitly implements the interface, TypeScript could infer these types without us having to redeclare them:
class UserServiceImpl implements UserService {
// Types could be inferred from the interface
async getUser(id) { ... }
async updateUser(user) { ... }
}
This would:
- Follow the DRY principle
- Reduce boilerplate
- Lower maintenance burden when types change
- Decrease chances of inconsistencies
- Support TypeScript's goal of type safety with minimal overhead
Is there any plan to implement this feature? It seems like a natural evolution of TypeScript's powerful type inference capabilities.
💻 Use Cases
- What do you want to use this for? Write cleaner code
- What shortcomings exist with current approaches? It would not be a breaking change
- What workarounds are you using in the meantime? No workarounds, still writing again the parameters types for functions