What causes the discrepancy between these two examples?
type Foo = { x: Foo }
and this:
type Bar<A> = { x: A }
type Foo = Bar<Foo>
// ^^^ Type alias 'Foo' circularly references itself
Aren't they supposed to have the same outcome?
What causes the discrepancy between these two examples?
type Foo = { x: Foo }
and this:
type Bar<A> = { x: A }
type Foo = Bar<Foo>
// ^^^ Type alias 'Foo' circularly references itself
Aren't they supposed to have the same outcome?
According to the official documentation, a type alias can reference itself in a property but not in any other part of the declaration:
A type alias can contain a reference to itself in a property.
So, as mentioned before, the following code is valid:
type Foo = { x: Foo }
On the contrary, it is not allowed for a type alias to be used elsewhere on the right side of the declaration.
For example, the below code will fail:
type Foo = Bar<Foo>
When it comes to the second scenario, it fails even without using the constraint:
type CustomType<T> = { property: string }
type AnotherType = CustomType<AnotherType> // still results in failure with a similar message
Essentially, the 2nd approach should look like this:
type CustomType = { property: AnotherType }
type AnotherType = CustomType;
This change makes it equivalent to the first method.
Furthermore, when using strictNullChecks, it seems impossible to initialize such a type.
According to the feedback from Jonathan, this solution proves to be effective:
interface RecursiveType {
[Key: string]: RecursiveType;
}
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