How can one implement inheritance from multiple classes using Generics?

Question

How can one implement inheritance from multiple classes using Generics?

I've been stuck on this problem for days and feel like I've exhausted my TypeScript skills. Any help would be greatly appreciated.

Although I have complex types, I'll try to simplify them for clarity.

Playground link

Imagine I have two classes, Score and Metric, each with two derived classes that need to implement different methods. The scores can inherit from a base class, but the Metrics must inherit from external classes that I don't own.

I tried using Mixins to define common methods in a class factory and apply constructors based on the implementations, but I'm struggling to get it to work.

So far, I've used interfaces A and B to distinguish between functionalities or as generic kinds extending A or B where shared functions exist.

Now, however, I need to use distinct constructors based on implementation rather than just types. While I don't require access to additional methods of derived classes, I must create objects at runtime inheriting the correct method from either A or B. It seems there might not be a solution for this, prompting me to consider alternative inheritance patterns beyond A and B.

If someone could verify if there's a workaround or offer a better abstraction pattern, I'd be extremely grateful.

typescript class inheritance mixins

Answer 1

Answer №1

After exploring various options, I eventually settled on implementing this code. While Kellys provided a helpful hint, I found that for my specific situation of dealing with multiple patterns where the primary difference lies in the "Kind," this approach worked more effectively. By passing an object of type Kind into the constructor (which is suitable for me as I can handle it in the constructors of subclasses)

interface X { isX:true}
interface Y { isY:true}

class BaseX {
    update(){/**do something */}
}

class BaseY {
    update(){/**do something else */}
}

interface Base{
    update:()=>void;//the methods here should be accessible when referencing a generic metric
}

type BaseConstructor = new (...args:any[])=>Base

function MetricFactory<MetricType extends BaseConstructor>(BaseZ:MetricType){
    return class extends BaseZ{
        commonMethod(){}
    }
}

class MetricY extends MetricFactory(BaseY){}
class MetricX extends MetricFactory(BaseX){
    someAdditionalMethod(){return this.commonMethod()}
}
function Metric<Kind extends X|Y>(kind:Kind) {
    return (kind as X).isX !== undefined ? new MetricX(): new MetricY() 
}

class Grade<Kind extends X|Y>{
    constructor(kind: Kind) {
        this.genericMetric = Metric(kind) as Kind extends X ? MetricX: MetricY
    }
    genericMetric: Kind extends X ? MetricX: MetricY
}

class GradeX extends Grade<X>{
    constructor(){super({isX:true})}
}

let myGrade = new GradeX()

myGrade.genericMetric.update() //does something
myGrade.genericMetric.commonMethod() //performs common action
myGrade.genericMetric.someAdditionalMethod() //executes additional step

Answer 2

After exploring various options, I eventually settled on implementing this code. While Kellys provided a helpful hint, I found that for my specific situation of dealing with multiple patterns where the primary difference lies in the "Kind," this approach worked more effectively. By passing an object of type Kind into the constructor (which is suitable for me as I can handle it in the constructors of subclasses)

interface X { isX:true}
interface Y { isY:true}

class BaseX {
    update(){/**do something */}
}

class BaseY {
    update(){/**do something else */}
}

interface Base{
    update:()=>void;//the methods here should be accessible when referencing a generic metric
}

type BaseConstructor = new (...args:any[])=>Base

function MetricFactory<MetricType extends BaseConstructor>(BaseZ:MetricType){
    return class extends BaseZ{
        commonMethod(){}
    }
}

class MetricY extends MetricFactory(BaseY){}
class MetricX extends MetricFactory(BaseX){
    someAdditionalMethod(){return this.commonMethod()}
}
function Metric<Kind extends X|Y>(kind:Kind) {
    return (kind as X).isX !== undefined ? new MetricX(): new MetricY() 
}

class Grade<Kind extends X|Y>{
    constructor(kind: Kind) {
        this.genericMetric = Metric(kind) as Kind extends X ? MetricX: MetricY
    }
    genericMetric: Kind extends X ? MetricX: MetricY
}

class GradeX extends Grade<X>{
    constructor(){super({isX:true})}
}

let myGrade = new GradeX()

myGrade.genericMetric.update() //does something
myGrade.genericMetric.commonMethod() //performs common action
myGrade.genericMetric.someAdditionalMethod() //executes additional step

How can one implement inheritance from multiple classes using Generics?

Answer №1

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