zepumph
commented
2 years ago Here is a snippet I made that gave me hope that Typescript itself is OK with provided less parameters for a callback. The issue seems to be about how the type inference is happening for Multilink. Furthermore Emitter is a great example of how we always provide the types, so perhaps that could be a worst-case.
```typescript
// Proof that callbacks support provided var args generally
class Hello {
decide( t: Parameters, callback: ( ...params: Parameters ) => void ): void {
callback( ...t );
}
}
// No type error
new Hello<[ boolean, boolean ]>().decide( [ true, true ], ( something: boolean, somethingAgain: boolean ) => { console.log( something, somethingAgain ); } );
// Type error because of three parameters
new Hello<[ boolean, boolean ]>().decide( [ true, true ], ( something: boolean, somethingAgain: boolean, somethingAgain2: boolean ) => { console.log( something, somethingAgain, somethingAgain2 ); } );
// No type error
new Hello<[ boolean, boolean ]>().decide( [ true, true ], ( something: boolean ) => { console.log( something ); } );
```
samreid
jonathanolson
@samreid and I ran into this while trying to figure out how to get rid of unused parameters in callbacks for DerivedProperty and Multilink (in https://github.com/phetsims/chipper/issues/1230). The current behavior is that you must provide the right types for the callback, because that is how the Parameter types are inferred. They aren't seeming to be inferred from the dependencies arrays (unfortunately).
Tagging @jonathanolson because he was the original converter to typescript.
Ideally we could specify any USED parameters needed for the callback, and they would have correct type information gathered from the list of dependencies provided.