CODEWITHSUNDEEP
lambdatypescriptabstractarrow-functionstypescript1.6
Craig Broadman
Craig Broadman

Reputation: 185

TypeScript abstract method using lambda/arrow function

I am using TypeScript 1.6 and would like to create an abstract class with an abstract method but use a lambda/arrow function in the concrete class.

Is this possible? The code shown below does not compile as it says

"Class 'Base' defines instance member function 'def', but extended class 'Concrete' defines it as instance member property"...

abstract class Base {
    abstract abc(): void;
    abstract def(): void;
}

class Concrete extends Base {
    private setting: boolean;

    public abc(): void  {
        this.setting = true;
    }

    public def = (): void => {
        this.setting = false;
    }
}

Upvotes: 8

Views: 5520

Answers (3)

user764754
user764754

Reputation: 4226

You can use an abstract property:

abstract class Base {    
    abstract def: () => void; // This is the abstract property
}

class Concrete extends Base {
    private setting: boolean;    

    public def = (): void => {
        this.setting = false;
    }
}

var myVar: Base = new Concrete();
myVar.def();
console.log((myVar as any).setting); // gives false

Upvotes: 2

Sergey Martynov
Sergey Martynov

Reputation: 406

You could do that starting typescript 2.0. In order to make that work you would need to declare a type for your arrow function

type defFuntion = () => void;

then declare 

abstract class Base {
    abstract abc(): void;
    abstract readonly def: defFuntion;
}

here is a reference for this feature

Upvotes: 0

Bruno Grieder
Bruno Grieder

Reputation: 29814

My understanding of Typescript specifications is that when you are declaring

public def = (): void => {
    this.setting = false;
}

You are actually declaring a property called def and not a method on the Base class.

Properties cannot (unfortunately IMHO) be abstracted in Typescript: https://github.com/Microsoft/TypeScript/issues/4669

Upvotes: 2

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