Utilizing Union Types as Constraints in Generic Type Parameters within TypeScript

Is it possible to create a generic class that is constrained by a union type? Consider the following scenario:

class Shoe {
    constructor(public size: number){}
}

class Dress {
    constructor(public style: string){}
}

class Box <T extends Shoe | Dress > {
}

Now, let's look at this example:

// since move can handle multiple boxes of either shoes or dresses
class Move<B extends Box<Shoe>[] | Box<Dress>[]> {
    private stuff: B;
    constructor(public toMove: Box<Shoe>[] | Box<Dress>[]) {
        this.stuff = toMove // this does not compile
    }

}

How can we make this work? Check out this Playground link illustrating the issue

Answer №1

I believe, based on my interpretation of your true intentions, that this solution should meet your needs:

class Shoe {
    constructor(public size: number){}
}

class Dress {
    constructor(public style: string){}
}

class Box <T extends Shoe | Dress > {
}


// due to the capability of moving multiple boxes containing either shoes or dresses
class Move<B extends Box<Shoe>[] | Box<Dress>[]> {
    private itemsToMove: B;
    constructor(public toMove: B) {
        this.itemsToMove = toMove;
    }

}

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