This gives an explanation of why they made the choice: https://github.com/Microsoft/TypeScript/wiki/FAQ#why-are-function-parameters-bivariant https://github.com

This gives an explanation of why they made the choice: https://github.com/Microsoft/TypeScript/wiki/FAQ#why-are-function-parameters-bivariant https://github.com/Microsoft/TypeScript/wiki/FAQ#why-are-fun... Also, FWIW, in my experience, I don't think I've ever actually run into a problem with this in real code.