Extending generic collection classes in Typescript

I'm researching some Typescript that won't compile, so I'm going to layout the problem here and I'll post the answer alter if/when I find it. (Answer Below!)

I have a base Generic which can accept strings, numbers, booleans, strings[] and numbers[]

export default class ParameterValue<
  T extends string | number | boolean | string[] | number[]
> {
  _val: T

  private setValue(newValue: T) {
    this._val = newValue
  }
}

I want to extend this to work with arrays specifically.

export default class ArrayParameterValue<
  T extends string | number
> extends ParameterValue<T[]> {

  private addValue(newValue: T) {
    if (!this._val.contains(newValue)) {
      this._val.push(newValue);
    }
  }
}

But I'm getting the following Typescript Error:

Type 'T[]' does not satisfy the constraint 'string | number | boolean | string[] | number[]'.
  Type 'T[]' is not assignable to type 'string[]'.
    Type 'T' is not assignable to type 'string'.
      Type 'string | number' is not assignable to type 'string'.
        Type 'number' is not assignable to type 'string'.ts(2344)

The Answer

I think the answer is that BaseParameter must accept type Array.

string[] and number[] can't either on their own accept

string | number

, so there's an error.

In fact I was able to make my code a bit tighter because I could remove string[] and number[] as types and replace them with

T extends string | number | boolean | Array<string | number>