Is it possible to meet the requirements of a specific interface using an enum field as the criteria?

I've been struggling to create a versatile function that can return a specific interface based on an enum argument, but all my attempts have failed.

Could it be possible that I missed something or am simply approaching it the wrong way?

If I try to typecast the result to that interface, everything works fine, but it doesn't serve much purpose for me.

enum Operations {
    Add = "add",
    Subtract = "subtract",
}

interface BaseAction {
    operation: Operations;
    timestamp: number;
}

interface AddAction extends BaseAction {
    operation: Operations.Add;
}

interface SubtractAction extends BaseAction {
    operation: Operations.Subtract;
}

type GenericAction = AddAction | SubtractAction;

const createAction = (operation: Operations) => ({
    operation,
    timestamp: new Date().getTime(),
});

const executeAction = (action: GenericAction) => {};

const action = createAction(Operations.Add);
executeAction(action);

Answer №1

There are two possible solutions:

  1. To resolve the issue, replace GenericRequest with BaseRequest in the sendRequest function and eliminate the GenericRequest type.
  2. Another workaround is to make the createRequest function generic:
    const createRequest = <TCommand extends Commands>(command: TCommand) => ({
        command,
        timestamp: new Date().getTime(),
    });
    
    This modification ensures that the command property corresponds to the type passed in the command argument.

The reason behind this recommendation is that createRequest now outputs an object with a command property of the entire Commands type, irrespective of the specific input type. On the other hand, using the GenericRequest type in the sendRequest function restricts the command property to only be of type InfoRequest or EchoRequest, without considering all values of the Command enum.

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