Overloading constructors in Typescript

Question

Overloading constructors in Typescript

I am struggling to convert these Java constructor overloads to Typescript:

public QueryMixin() {
    this(null, new DefaultQueryMetadata(), true);
}

public QueryMixin(QueryMetadata metadata) {
    this(null, metadata, true);
}

public QueryMixin(QueryMetadata metadata, boolean expandAnyPaths) {
    this(null, metadata, expandAnyPaths);
}

public QueryMixin(T self) {
    this(self, new DefaultQueryMetadata(), true);
}

public QueryMixin(T self, QueryMetadata metadata) {
    this(self, metadata, true);
}

public QueryMixin(T self, QueryMetadata metadata, boolean expandAnyPaths) {//...}

I have attempted to create these constructors by referencing the examples provided, but I am unable to resolve the issue...

Do you have any suggestions?

constructor();  <<<1>>>
constructor(metadata: QueryMetadata);
constructor(metadata: QueryMetadata, expandAnyPaths: boolean);
constructor(self: T);
constructor(self: T, metadata: QueryMetadata);
constructor(selfOrMetadata: T | QueryMetadata, expandAnyPaths: boolean) {
    this.self = selfOrMetadata;  <<< PROBLEM HERE
    this.metadata = selfOrMetadata;  <<< PROBLEM HERE
    this.expandAnyPaths = expandAnyPaths;
}

The compilation message at <<<1>>> states:

Overload signature is not compatible with function implementation.

typescript typescript2.0

Answer 1

Answer №1

To achieve the constructor overloads you desire, it is necessary to perform type checking in order to make it possible. While I am not aware of the exact structure of QueryMetadata, the concept can be grasped from this self-contained example.

A custom type guard is utilized here to differentiate between union types:

interface QueryMetadata {
    metadata: string;
}

function isQueryMetadata(obj: any): obj is QueryMetadata {
    return (obj && obj.metadata);
}

class Example<T> {

    private metadata: QueryMetadata;
    private self: T;
    private expandAnyPaths: boolean;

    constructor(metadata: QueryMetadata);
    constructor(metadata: QueryMetadata, expandAnyPaths: boolean);
    constructor(self: T);
    constructor(self: T, metadata: QueryMetadata);
    constructor(selfOrMetadata: T | QueryMetadata, expandOrMetadata: boolean | QueryMetadata = false) {
        if (isQueryMetadata(selfOrMetadata)) {
            this.metadata = selfOrMetadata;
        } else {
            this.self = selfOrMetadata;
        }

        if (isQueryMetadata(expandOrMetadata)) {
            this.metadata = expandOrMetadata;
        } else {
            this.expandAnyPaths = expandOrMetadata;
        }
    }
}

Factory Method Approach

If starting anew, utilizing a factory method to construct your class may be preferable...

interface QueryMetadata {
    metadata: string;
}

class Example<T> {

    private metadata: QueryMetadata;
    private self: T;
    private expandAnyPaths: boolean;

    protected constructor() { }

    static fromMetadata<T>(metadata: QueryMetadata, expandAnyPaths: boolean = false) {
        const example = new Example<T>();
        example.metadata = metadata;
        example.expandAnyPaths = expandAnyPaths;
    }

    static fromSelf<T>(self: T, expandAnyPaths: boolean = false) {
        const example = new Example<T>();
        example.self = self;
        example.expandAnyPaths = expandAnyPaths;
    }
}

const example1 = Example.fromSelf('Some Value');
const example2 = Example.fromSelf('Some Value', true);
const example3 = Example.fromMetadata({ metadata: 'val' });
const example4 = Example.fromMetadata({ metadata: 'val' }, true);

Answer 2

To achieve the constructor overloads you desire, it is necessary to perform type checking in order to make it possible. While I am not aware of the exact structure of QueryMetadata, the concept can be grasped from this self-contained example.

A custom type guard is utilized here to differentiate between union types:

interface QueryMetadata {
    metadata: string;
}

function isQueryMetadata(obj: any): obj is QueryMetadata {
    return (obj && obj.metadata);
}

class Example<T> {

    private metadata: QueryMetadata;
    private self: T;
    private expandAnyPaths: boolean;

    constructor(metadata: QueryMetadata);
    constructor(metadata: QueryMetadata, expandAnyPaths: boolean);
    constructor(self: T);
    constructor(self: T, metadata: QueryMetadata);
    constructor(selfOrMetadata: T | QueryMetadata, expandOrMetadata: boolean | QueryMetadata = false) {
        if (isQueryMetadata(selfOrMetadata)) {
            this.metadata = selfOrMetadata;
        } else {
            this.self = selfOrMetadata;
        }

        if (isQueryMetadata(expandOrMetadata)) {
            this.metadata = expandOrMetadata;
        } else {
            this.expandAnyPaths = expandOrMetadata;
        }
    }
}

Factory Method Approach

If starting anew, utilizing a factory method to construct your class may be preferable...

interface QueryMetadata {
    metadata: string;
}

class Example<T> {

    private metadata: QueryMetadata;
    private self: T;
    private expandAnyPaths: boolean;

    protected constructor() { }

    static fromMetadata<T>(metadata: QueryMetadata, expandAnyPaths: boolean = false) {
        const example = new Example<T>();
        example.metadata = metadata;
        example.expandAnyPaths = expandAnyPaths;
    }

    static fromSelf<T>(self: T, expandAnyPaths: boolean = false) {
        const example = new Example<T>();
        example.self = self;
        example.expandAnyPaths = expandAnyPaths;
    }
}

const example1 = Example.fromSelf('Some Value');
const example2 = Example.fromSelf('Some Value', true);
const example3 = Example.fromMetadata({ metadata: 'val' });
const example4 = Example.fromMetadata({ metadata: 'val' }, true);

Overloading constructors in Typescript

Answer №1

Factory Method Approach

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