Mixin with abstract class infers wrong type for super

🔎 Search Terms

"mixin abstract super", "mixin abstract super type", "mixin abstract constructor super", "mixin abstract constructor super type", "mixin Abstract method cannot be accessed via super expression"

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about "super"

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.7.0-dev.20241022#code/IYIwzgLgTsDGEAJYBthjAgsgTwILmjggGFV0EBvAKAQQAcBXEZAS1gVEhngQHMBTCADlgAW34AKAJQAuBFxYA7XgG4qAXypUAZg0XwWAe0UJRLAB5KA6iwgALfFyKk0YADwAVAEJp+CfuYQ-IoAJhiK-ADuCBIAdPHAULxgcsCK2ADaALpSCAC8AHxYeATcJGRgBRIA+iC+ct6+udQ0SBVYFkou5AFBoRi1vpRatLSMzGx8giLi0nIKysOjo1CCDFAmYAx0-FCxAsJiklIqCAD0ZwgAolBQhlByAESOhDzi9oYhCADkBzP83wQSjarh+OBeZW6YEBsDSikMiBAfjgsH46H4XwAbixgPJtrt-OY6Kt0EZFLFHq1aJpqSMEKsIOsTJhOoooWpNFoqEoglBtHA-DgAJKKXn81FLKaHWayeTQJSqDRaXT6CBk0ysmz2EVigWeHxgPy9YJhBARaJxBJJFIcdLZXKFYo63bi-hVQaGhoG-jNOkoUEsyxs9rG-oID1+FrLcasdh-I5zOVQBWS5YMpl4nZ7eMy04XBCRe4AazAVIQNPLdPTGw6QfZGiAA

💻 Code

abstract class MyAbstractClass {
  public abstract getName(): string;
}

function mixinWithAbstractClass<TBase extends new (...args: any[]) => MyAbstractClass>(_base: TBase) {

  class MixinClass extends _base {
    public getName(): string {
      return super.getName(); // Error: "Abstract method 'getName' in class 'MyAbstractClass' cannot be accessed via super expression."
    }
  }

  return MixinClass;
}



interface MyInterface {
  getName(): string;
}

function mixinWithInterface<TBase extends new (...args: any[]) => MyInterface>(_base: TBase) {

  class MixinClass extends _base {

    public getName(): string {
      return super.getName(); // works as expected
    }
  }

  return MixinClass;
}

🙁 Actual behavior

mixinWithAbstractClass fails because the compiler infers that super is of the exact type class MyAbstractClass.

🙂 Expected behavior

I expected mixinWithAbstractClass to compile like mixinWithInterface does. The constraint TBase extends new (...args: any[]) => MyAbstractClass specifies that TBase extends a concrete constructor, which returns instances that conform to MyAbstractClass. Since the constructor is concrete, we can infer that TBase (the superclass) already implements the abstract methods.

Additional information about the issue

No response

Inizia con la riproduzione collegata di TypeScript Playground e confronta i casi mixinWithAbstractClass e mixinWithInterface, concentrandoti su come il compilatore determina il tipo di super. Traccia il percorso del controllo dei tipi per i metodi astratti in una classe generica che estende _base; il lavoro è completato quando il mixin di classe astratta accetta super.getName() senza introdurre una regressione nel caso dell’interfaccia, con un test di regressione per la riproduzione.