What TypeScript syntax is similar to Java's "? extends MyClass" when using generics?

How can we indicate the TypeScript equivalent of Java's ? extends MyClass?

One possible way to achieve this is:

function myFunc <TComponent extends MyBaseClass>(param: ComponentFixture<TComponent>) {}

Is there a more concise alternative such as:

function myFunc(param: ComponentFixture<? extends MyBaseClass>) {} // This results in error TS1138: Parameter declaration expected

Any suggestions or insights on how to approach this issue?

Could it be that this feature has not been implemented yet?

Alternatively, is there a different syntax for achieving the same functionality?

What might be the reasoning behind the lack of support for this feature?

javatypescriptgenericscovariance

Answer №1

At this moment, TypeScript does not support that specific syntax. You're welcome to propose the idea to the TypeScript team.

However, considering their current workload, it's likely to be given a lower priority.

Answer №2

To ensure a default value is set for a generic type as MyBaseClass inside a ComponentFixture, you can utilize the following syntax:

type ComponentFixture<TComponent extends MyBaseClass=MyBaseClass> = {...}

function myFunc (param: ComponentFixture) {}

This approach guarantees that if no specific generic arguments are provided within <>, typescript will automatically resort to using the default type of MyBaseClass.

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