What specific category does the enum object fall under?

Question

What specific category does the enum object fall under?

How can I create a wrapper class for a collection of elements in an enumeration?

export class Flags<ENUMERATION> {

    items = new Set<ENUMERATION>();

    enu;                // what type ?

    constructor(enu) {     // what type ?
        this.enu=enu;
    }

    set(id:ENUMERATION) { this.items.add(id); return this; }

     // For use: determine if a specific value is part of the enum or not
    setChecking(id:string):boolean{
        if (id in this.enu){
            let item = this.enu[id];
            this.items.add(item);
            return true;
        }
        return false;
    }
  // .....
}

Example:

    enum Props{ One, Two, Three };
    let fls=new U.Flags<Props>(Props);
    fls.set(Props.One);
    fls.set("asdf");          // TypeScript detects the wrong value
    fls.set(Props.Two);
    if (!fls.setChecking("xxxx"))  // Check external string against the enum set
        throw error

Question: What are the types of the 'enu' property and the parameter in the constructor, what is the type of the enum object?

If we specify the type in the constructor, we could write:

  let fls=new U.Flags(Props);

(TypeScript would infer the type from the constructor specification)

typescript generics typing

Answer 1

Answer №1

To represent the enum container object instead of the enum, you can modify the type parameter. The specific type of the enum would be

ENUMERATION[keyof ENUMERATION]>

export class Switcher<ENUMERATION extends { [P in keyof ENUMERATION]: any}> {

    options = new Set<ENUMERATION[keyof ENUMERATION]>();

    en: ENUMERATION;                // what type ?

    constructor(en: ENUMERATION) {     // what type ?
        this.en=en;
    }

    select(choice:ENUMERATION[keyof ENUMERATION]) { this.options.add(choice); return this; }

    // usage example: a random string points to an enum element or is not allowed
    validateSelection(value:string):boolean{
        if (value in this.en){
            let chosen = this.en[value as keyof ENUMERATION];
            this.options.add(chosen);
            return true;
        }
        return false;
    }
// .....
}

enum Choices{ First, Second, Third };
let swt=new Switcher(Choices);
swt.select(Choices.First);
swt.select("something");          // TypeScript picks up on the incorrect value
swt.select(Choices.Second);
if (!swt.validateSelection("invalid"))  // A separate string can be validated against the set/enum
{

}

Answer 2

To represent the enum container object instead of the enum, you can modify the type parameter. The specific type of the enum would be

ENUMERATION[keyof ENUMERATION]>

export class Switcher<ENUMERATION extends { [P in keyof ENUMERATION]: any}> {

    options = new Set<ENUMERATION[keyof ENUMERATION]>();

    en: ENUMERATION;                // what type ?

    constructor(en: ENUMERATION) {     // what type ?
        this.en=en;
    }

    select(choice:ENUMERATION[keyof ENUMERATION]) { this.options.add(choice); return this; }

    // usage example: a random string points to an enum element or is not allowed
    validateSelection(value:string):boolean{
        if (value in this.en){
            let chosen = this.en[value as keyof ENUMERATION];
            this.options.add(chosen);
            return true;
        }
        return false;
    }
// .....
}

enum Choices{ First, Second, Third };
let swt=new Switcher(Choices);
swt.select(Choices.First);
swt.select("something");          // TypeScript picks up on the incorrect value
swt.select(Choices.Second);
if (!swt.validateSelection("invalid"))  // A separate string can be validated against the set/enum
{

}

What specific category does the enum object fall under?

Answer №1

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