EC

Effect Community•3mo ago•

2 replies

Enrico Secondulfo

Handling generics in Context.Tag for dynamic permissions

Hi all,
I've only recently dived into the fantastic world of Effect.
I was studying Lucas Barake's great content, specifically https://lucas-barake.github.io/building-a-composable-policy-system/.
I decided to create a policy system that is as generic as possible. The problem arises here:

export type PermissionAction = "read" | "manage" | "delete";
export type PermissionConfig = Record<string, ReadonlyArray<PermissionAction>>;

export type InferPermissions<T extends PermissionConfig> = {
[K in keyof T]: T[K][number] extends PermissionAction
?

${K & string}:${T[K][number]}

${K & string}:${T[K][number]}

: never;
}[keyof T];

export const buildPermissions = <T extends PermissionConfig>(
config: T,
): Array<InferPermissions<T>> => {
return Object.entries(config).flatMap(([domain, actions]) =>
actions.map((action) =>

${domain}:${action}

${domain}:${action}

as InferPermissions<T>),
);
};

type Policy<E, R> = Effect.Effect<void, HttpApiError.Forbidden | E, R>;

I've gotten stuck at a specific point (https://github.com/lucas-barake/effect-monorepo/blob/07c09dc6620847017aba7fa646ec22549a774247/packages/domain/src/Policy.ts#L27C14-L27C25):
export class CurrentUser extends Context.Tag("CurrentUser")<
CurrentUser,
{
readonly sessionId: string;
readonly userId: UserId;
readonly permissions: Set<Permission>;
}
>() {}

const Permissions = internal.makePermissions({
__test: ["read", "manage", "delete"],
} as const);

export const Permission = Schema.Literal(...Permissions).annotations({
identifier: "Permission",
});
export type Permission = typeof Permission.Type;

In this case, permissions are defined using the Permission type, but I need to make everything generic to ensure the code is reusable. I understand—correct me if I'm wrong—that it's not possible to use generics directly with Context.Tag.
How can I achieve this?

Thank you

Building a Composable Policy System in TypeScript with Effect

In this guide, we'll build a composable, type-safe, and scalable access control system in TypeScript and Effect.

GitHub

effect-monorepo/packages/domain/src/Policy.ts at 07c09dc6620847017a...

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