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Description
TypeScript Version: 3.8.2
Search Terms: structure, resolve, compare, equality, type, mismatch, circular, tuple, cycle, recursive
Code
I'm trying to represent some type information for runtime use. I define the following enum:
enum Type {
Int = "Int",
List = "List",
}
And I define a Codec
type: a tuple, within which the first element is the given Type
enum value, and the second element––which is optional––is another Codec
:
type Codec<
T extends Type,
C extends Codec<Type> | undefined = undefined
> = C extends undefined ? [T] : [T, C];
I'm able to assign Codec
s as expected:
const c1: Codec<Type.Int> = [Type.Int];
const c2: Codec<Type.List, Codec<Type.Int>> = [Type.List, [Type.Int]];
And I'm able to create helpers for the Type.Int
Codec
:
type IntCodec = Codec<Type.Int>;
const createIntCodec = (): IntCodec => [Type.Int];
const intCodec = createIntCodec(); // signature is `[Type.Int]`
However, I'm unable to create helpers for Codec
s which nest other Codec
s:
type ListCodec<C extends Codec<Type>> = Codec<Type.List, C>;
const createListCodec = <C extends Codec<Type>>(of: C): ListCodec<C> => [Type.List, of]; // error
This results in an error: Type '[Type.List, C]' is not assignable to type 'Codec<Type.List, C>'. ts(2322)
.
Any thoughts would be greatly appreciated! Thank you!