Utilizing Typescript to create overload cascade constructors

Question

Utilizing Typescript to create overload cascade constructors

I am facing a challenge in translating 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) {
    this.self = self;
    this.metadata = metadata;
    this.expandAnyPaths = expandAnyPaths;
}

Despite my attempts to create constructors by referring to the examples provided, I have not been able to successfully implement them...

Do you have any suggestions or ideas?

constructor();
constructor(metadata: QueryMetadata);
constructor(metadata: QueryMetadata, expandAnyPaths: boolean);
constructor(self: T);
constructor(self: T, metadata: QueryMetadata);
constructor(???) {
    this.self = self;  <<< ???
    this.metadata = selfOrMetadata;  <<< ???
    this.expandAnyPaths = expandAnyPaths;
}

typescript typescript2.0

Answer 1

Answer №1

It appears that the desired functionality involves supporting a wide range of parameter combinations, with default values for simplicity. When dealing with 3 parameters, there is a total of 8 possible on/off configurations. While TypeScript does offer function overloading capabilities, creating 8 overload variations for each combination may not be the most efficient approach from a maintenance perspective.

By utilizing named parameters instead of positional ones, the implementation process can be streamlined. This allows for easy addition of new parameters without having to create multiple overloaded functions exponentially.

interface QueryOptions { }
class DefaultQueryOptions implements QueryOptions { }

interface QuerySettings<T> {
    targetEntity: T;
    options: QueryOptions;
    enablePathExpansion: boolean;
}

class QueryHandler<T> implements QuerySettings<T> {
    targetEntity: T;
    options: QueryOptions;
    enablePathExpansion: boolean;

    constructor({
        targetEntity = null,
        options = new DefaultQueryOptions(),
        enablePathExpansion = true,
        }: Partial<QuerySettings<T>>> = {}) {
        this.targetEntity = targetEntity;
        this.options = options;
        this.enablePathExpansion = enablePathExpansion;
        console.log(this);
    }
}

// Any parameter combination is supported
new QueryHandler();
new QueryHandler({});
new QueryHandler({ targetEntity: {} });
new QueryHandler({ targetEntity: {}, options: {} });
new QueryHandler({ targetEntity: {}, options: {}, enablePathExpansion: false });
new QueryHandler({ targetEntity: {}, enablePathExpansion: false });
new QueryHandler({ options: {} });
new QueryHandler({ options: {}, enablePathExpansion: false });
new QueryHandler({ enablePathExpansion: false });

Experiment with it in TypeScript Playground

Answer 2

It appears that the desired functionality involves supporting a wide range of parameter combinations, with default values for simplicity. When dealing with 3 parameters, there is a total of 8 possible on/off configurations. While TypeScript does offer function overloading capabilities, creating 8 overload variations for each combination may not be the most efficient approach from a maintenance perspective.

By utilizing named parameters instead of positional ones, the implementation process can be streamlined. This allows for easy addition of new parameters without having to create multiple overloaded functions exponentially.

interface QueryOptions { }
class DefaultQueryOptions implements QueryOptions { }

interface QuerySettings<T> {
    targetEntity: T;
    options: QueryOptions;
    enablePathExpansion: boolean;
}

class QueryHandler<T> implements QuerySettings<T> {
    targetEntity: T;
    options: QueryOptions;
    enablePathExpansion: boolean;

    constructor({
        targetEntity = null,
        options = new DefaultQueryOptions(),
        enablePathExpansion = true,
        }: Partial<QuerySettings<T>>> = {}) {
        this.targetEntity = targetEntity;
        this.options = options;
        this.enablePathExpansion = enablePathExpansion;
        console.log(this);
    }
}

// Any parameter combination is supported
new QueryHandler();
new QueryHandler({});
new QueryHandler({ targetEntity: {} });
new QueryHandler({ targetEntity: {}, options: {} });
new QueryHandler({ targetEntity: {}, options: {}, enablePathExpansion: false });
new QueryHandler({ targetEntity: {}, enablePathExpansion: false });
new QueryHandler({ options: {} });
new QueryHandler({ options: {}, enablePathExpansion: false });
new QueryHandler({ enablePathExpansion: false });

Experiment with it in TypeScript Playground

Answer 3

Answer №2

In TypeScript, you have the ability to define multiple signatures for a method or constructor while retaining a single implementation. The responsibility lies with the implementation to determine which overload has been invoked.

For instance, in your scenario, it could be structured like this:

constructor();
constructor(metadata: QueryMetadata);
constructor(metadata: QueryMetadata, expandAnyPaths: boolean);
constructor(self: T);
constructor(self: T, metadata: QueryMetadata);
constructor() {
    let self: T = null;
    let metadata : QueryMetadata = null;
    let expandAnyPaths = true;
    if(arguments.length > 0) {
        // Assuming QueryMetadata is a class
        if(arguments[0] instanceof QueryMetadata) { 
            expandAnyPaths = arguments[1] || true;
            metadata = arguments[0];
        }
        else {
            self = arguments[0]
            metadata = arguments[1];
        }
    }

    this.self = self;
    this.metadata = metadata || new DefaultQueryMetadata();;
    this.expandAnyPaths = expandAnyPaths;
}

Note: The implementation signature remains hidden from external entities (not considered in resolution when seeking the appropriate constructor). That's why we see the empty constructor signature twice – once for public use and again as the implementation signature.

Answer 4

In TypeScript, you have the ability to define multiple signatures for a method or constructor while retaining a single implementation. The responsibility lies with the implementation to determine which overload has been invoked.

For instance, in your scenario, it could be structured like this:

constructor();
constructor(metadata: QueryMetadata);
constructor(metadata: QueryMetadata, expandAnyPaths: boolean);
constructor(self: T);
constructor(self: T, metadata: QueryMetadata);
constructor() {
    let self: T = null;
    let metadata : QueryMetadata = null;
    let expandAnyPaths = true;
    if(arguments.length > 0) {
        // Assuming QueryMetadata is a class
        if(arguments[0] instanceof QueryMetadata) { 
            expandAnyPaths = arguments[1] || true;
            metadata = arguments[0];
        }
        else {
            self = arguments[0]
            metadata = arguments[1];
        }
    }

    this.self = self;
    this.metadata = metadata || new DefaultQueryMetadata();;
    this.expandAnyPaths = expandAnyPaths;
}

Note: The implementation signature remains hidden from external entities (not considered in resolution when seeking the appropriate constructor). That's why we see the empty constructor signature twice – once for public use and again as the implementation signature.

Utilizing Typescript to create overload cascade constructors

Answer №1

Answer №2

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