microsoft / microsoft/TypeScript

ConstructorOf<T> wrapper to declare type of constructor of type parameter

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Description

so if I have

class MyClass {
}

Then the type of MyClass.prototype is MyClass
And the type of MyClass is typeof MyClass

If I want these two functions

function takesPrototype(p: MyClass) { /* ... */ }
function takesClass(p: typeof MyClass) { /* ... */ }

I can call them as

takesPrototype(MyClass.prototype)
takesClass(MyClass)

But what if MyClass was defined as a type parameter.
For example if I want to have a function that of this type -

const mod = getModule(ModuleClass)
// mod should be of type ModuleClass

I would like to define this as such

function getModule<M extends Module>(moduleClass: typeof M): M {
 // something like a getInstance() pattern
}

The problem with this is typeof M will complain that I am trying to use M as a value while it is a type.

So I suggest a type wrapper of this type

type ConstructorOf<C> = { new( ...args: any[] ): C }

Now I can define my function as such

function getModule<M extends Module>(moduleClass: ConstructorOf<M>): M {
 // something like a getInstance() pattern
}

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reviewing the issue's proposed ConstructorOf wrapper and the existing distinction between type parameters and constructor values in TypeScript. Determine the type-system and compiler entry points involved, then define the supported generic-constructor behavior and validate it with focused type-checking tests covering getModule and constructor arguments.

Written by the indexing model from the issue text.

Assessment

Tech stack
typescript
Domain
compilers
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
25/100

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