Cannot use 'new' error on intersection type with constructor

tsc: 2.4.2

class X { }
declare interface ConstructorAnyArgs<TClass> {
    new (...args: any[]): TClass
}


function foo(): ConstructorAnyArgs<X> { return }
function boo(): ConstructorAnyArgs<X> & { superclass: any } { return }

let Y = foo()
let y = new Y()

let Z = boo()
let z = new Z() // Cannot use 'new' with an expression whose type lacks a call or construct signature.

http://www.typescriptlang.org/play/index.html#src=class%20X%20%7B%20%7D%0D%0Adeclare%20interface%20ConstructorAnyArgs%3CTClass%3E%20%7B%0D%0A%20%20%20%20new%20(...args%3A%20any%5B%5D)%3A%20TClass%0D%0A%7D%0D%0A%0D%0A%0D%0Afunction%20foo()%3A%20ConstructorAnyArgs%3CX%3E%20%7B%20return%20%7D%0D%0Afunction%20boo()%3A%20ConstructorAnyArgs%3CX%3E%20%26%20%7B%20superclass%3A%20any%20%7D%20%7B%20return%20%7D%0D%0A%0D%0Alet%20Y%20%3D%20foo()%0D%0Alet%20y%20%3D%20new%20Y()%0D%0A%0D%0Alet%20Z%20%3D%20boo()%0D%0Alet%20z%20%3D%20new%20Z()%20%2F%2F%20Cannot%20use%20'new'%20with%20an%20expression%20whose%20type%20lacks%20a%20call%20or%20construct%20signature.%0D%0A

This regressed between 2.1 and 2.2

Mohamed Hegazy (@mhegazy)

Mohamed Hegazy (@mhegazy) Ryan Cavanaugh (@RyanCavanaugh)

Adding this from StackOverflow for completeness

I have identified a problem when using intersection types in TypeScript...

I have three type aliases:

Prototype<T> - expresses an object/class that has a prototype property.
DefaultCtor<T> - expresses an object/class with a default constructor.
ParameterizedCtor<T> expresses an object/class with a parameterized constructor.

I have tried these intersection permutations:

Prototype<T> & DefaultCtor<T> - works fine.
Prototype<T> & ParameterizedCtor<T> - raises a compiler error.

Example

type Prototype<T> = {
    prototype: T;
}

type DefaultCtor<T> = {
    new(): T;
}

type ParameterizedCtor<T> = {
    new(...args: any[]): T
}

function makeDefault<T>(ctor: Prototype<T> & DefaultCtor<T>): T {
    return new ctor();
}

function makeWithArgs<T>(ctor: Prototype<T> & ParameterizedCtor<T>, ...args: any[]): T {
    return new ctor(...args);
    // ERROR: Cannot use 'new' with an expression whose type lacks a call or construct signature.
}

Try it in the Playground

Error
The error occurs with the Prototype<T> & ParameterizedCtor<T> intersection:

Cannot use 'new' with an expression whose type lacks a call or
construct signature.

Why does the TypeScript compiler recognise the Prototype<T> & DefaultCtor<T> intersection type as having a constructor, but not the Prototype<T> & ParameterizedCtor<T> intersection type?

I may be running into this as well. Here's my example:

declare namespace __example {
  interface A {
    aProp;
  }

  interface AConstructor {
    new(): A;
  }

  export const A: AConstructor;
}

class MyClass {
  myInvalidFunc = (A: __example.A) => {
    // [ts] Cannot use 'new' with an expression whose type lacks a call or construct signature.
    const a: __example.A = new A();
  }

  myValidFunc = (A: __example.AConstructor) => {
    const a: __example.A = new A();
  }
}

myInvalidFunc = (A: __example.A) => {
// [ts] Cannot use 'new' with an expression whose type lacks a call or construct signature.
const a: __example.A = new A();
}

This is correct. __example.A isn't a constructor.

Fix mixin logic to preserve at least one constructor type even when the

A silly mistake in the logic for handling mixin classes. Fix is in #27701.

Fix mixin logic to preserve at least one constructor type even when the

Fix mixin logic to preserve at least one constructor type even when t…

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Cannot use 'new' error on intersection type with constructor #17388

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Cannot use 'new' error on intersection type with constructor #17388

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RyanCavanaugh commented on Jul 25, 2017

MrMatthewLayton commented on Mar 27, 2018

gssjr commented on Jun 15, 2018

weswigham commented on Jun 15, 2018

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mattmccutchen commented on Oct 11, 2018

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