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Question

How do I nest the same type that uses generics?

interface programConfig<T extends Record<string, any>> {
  // other types removed; not relevant to the question
  commands?: { [key: string]: programConfig<???> }; // how do I type this?
}

More complete ts playground example that shows what I'm trying to accomplish

Answer 1

You can specify a second generic to encompass the sub elements of the programConfig, in this example I constrained the inner ones to not allow a 3rd level of nesting since supporting arbitrary nesting would be annoying and hopefully not necessary

playground

interface BaseProgramConfig<T extends Record<string, unknown> >{
  options?: {
    [K in keyof T]: {
      validator?: () => T[K]
    }
  },
  handler?: (data: T) => void
}
interface programConfigWithCommands<T extends Record<string, unknown>, Sub extends Record<string, Record<string, unknown>>> extends BaseProgramConfig<T> {
  commands?: {[K in keyof Sub]: BaseProgramConfig<Sub[K]>}
}

class Program<T extends Record<string, unknown>, Comms extends Record<string, Record<string, unknown>>> {
  constructor(config: programConfigWithCommands<T,Comms>) { }
}

const foo = new Program({
  options: {
    'fruit': { validator: () => 'asdf' },
    'animal': { validator: Number },
  },
  handler: ({ fruit, animal, thing }) => { // fruit and animal are properly typed based on options above
    console.log(fruit, animal)
  },
  commands: {
    foo: {
      options: {
        'tree': { validator: () => 'asdf' },
        'person': {},
      },
      handler: ({ tree, person, thing }) => { // tree is typed as string, person is typed as unknown
        console.log(tree, person)
      },
    }
  }
});

Answer 2

You just need to call new Program again, like here:

type programConfig<T extends Record<string, any> = Record<string, any>> = {
  options?: {
    [K in keyof T]: {
      validator?: () => T[K]
    }
  },
  handler?: (data: T) => void,
  commands?: { [key: string]: Program<Record<string,unknown>> }; // here use sub-programs that have nothing to do with T
}

class Program<T extends Record<string, any> = Record<string, any>> {
  constructor(config: programConfig<T>) { }
}

const foo = new Program({
  options: {
    'fruit': { validator: () => 'asdf' },
    'animal': { validator: Number },
  },
  handler: ({ fruit, animal, thing }) => { // fruit and animal are properly typed based on options above
    console.log(fruit, animal)
  },
  commands: {
    foo: new Program({
      options: {
        'tree': { validator: () => 'asdf' },
        'person': {},
      },
      handler: ({ tree, person, thing }) => { // tree and person are typed in the same way and Program of any type is accepted in commands
        console.log(tree, person)
      },
    })
  }
});

Playground