infer argument types for generic method decorator factory

[rhyek]

Search Terms

TypedPropertyDescriptor generic method decorator arguments

Suggestion

I would like for a method decorator factory to be able to receive a callback as an argument whose own arguments mirror the method the decorator is being applied to.

Use Cases

I would like to write a custom memoize decorator for methods that allows me to provide a function which would return a cache key based on the original method's arguments.

Examples

function cached<TargetType extends Object, ArgumentsType extends any[], ReturnType = any>(cacheKey: (...args: ArgumentsType) => string) {
  return function(
    target: any,
    key: PropertyKey,
    descriptor: TypedPropertyDescriptor<(...params: ArgumentsType) => Promise<ReturnType>>
  ) {
    descriptor.value = async function(this: TargetType, ...args: ArgumentsType) {
      const _cacheKey = cacheKey(...args);
      const result = getFromCache(_cacheKey) ?? descriptor.value.apply(this, ...args);
      return result;
    }
  }
}

class Example {
  @cached(param1 => param1.toUpperCase()) // should know param1 is of type string
  async work(param1: string) {
    return networkRequest(param1);
  }
}

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.

[RyanCavanaugh]

We're not expanding the current experimental decorator implementation any further since this is something we're trying to standardize through the TC39 proposal. Suggestions for more behavior there should be taken to the tc39 proposal repo