Type / Enum / Dict Skill

This skill covers three tightly-related artifacts created together whenever a domain concept needs a constrained string type at compile time and/or at runtime.

The three artifacts

Type (src/type/T{Name}.ts)

Pure TypeScript — no runtime value. Three variants:

String union — for finite known values:

type TPublishState = "draft" | "published";
export default TPublishState;

Template literal — for structured string shapes validated statically by the type system:

type TSimpleDate = `${number}-${number}-${number}`;
export default TSimpleDate;

Namespace-augmented — when sub-groups of the union are useful independently:

type TContentType =
  | TContentType.Raster
  | TContentType.Vector;

namespace TContentType {
  export type Raster = "image/png" | "image/jpeg";
  export type Vector = "image/svg+xml";
}
export default TContentType;

Template literal types generally don't need an Enum or Desc — there are no finite members to enumerate.

---

Enum (src/enum/{Name}Enum.ts)

Runtime identity record: every key equals its value. Relies on the global utility type Enum<T> = { [K in T]: K } (no import needed — it's a global declaration).

import TPublishState from "../type/TPublishState.js";

const PublishStateEnum: Enum<TPublishState> = {
  draft: "draft",
  published: "published",
};
export default PublishStateEnum;

Use Object.values(SomeEnum) to get an array of all members at runtime.

The type source can also come from a DTO interface member instead of a dedicated type file:

import IMyDto from "../dto/IMyDto.js";
const MyRoleEnum: Enum<IMyDto.Role> = { admin: "admin", viewer: "viewer" };

---

Dict (src/dict/{Name}Desc.ts)

Maps every union member to a string. Relies on the global utility type Desc<T> = { [K in T]: string }. Prefer using the enum constants as computed keys — this avoids magic strings and ensures the dict stays in sync with the enum.

Label dict — human-readable display values:

import TPublishState from "../type/TPublishState.js";
import PublishStateEnum from "../enum/PublishStateEnum.js";

const PublishStateDesc: Desc<TPublishState> = {
  [PublishStateEnum.draft]: "Draft",
  [PublishStateEnum.published]: "Published",
};
export default PublishStateDesc;

Value-mapping dict — when the mapped value is not a label (e.g. file extension, icon name, color):

// Name the file to signal the mapping direction: {Target}From{Source}.ts
const ExtensionFromContentType: Desc<TContentType> = {
  "image/png": "png",
  "image/svg+xml": "svg",
};
export default ExtensionFromContentType;

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File naming conventions

Artifact	File	Export name
Type	src/type/T{Name}.ts	TName (default)
Enum	src/enum/{Name}Enum.ts	{Name}Enum (default)
Label dict	src/dict/{Name}Desc.ts	{Name}Desc (default)
Value-mapping dict	src/dict/{Target}From{Source}.ts	descriptive (default)

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Barrel exports

Always update the barrel index after creating a file.

src/type/index.ts — type-only re-exports:

export type { default as TPublishState } from "./TPublishState.js";

src/enum/index.ts and src/dict/index.ts — value re-exports:

export { default as PublishStateEnum } from "./PublishStateEnum.js";
export { default as PublishStateDesc } from "./PublishStateDesc.js";

---

Path aliases

Use the package's configured path alias for cross-directory imports (e.g. ~/type/..., ~/enum/...). Check tsconfig.json for the alias prefix — don't hardcode deep relative paths.

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Decision guide

Situation	What to create
Finite string values (states, phases, categories)	Type + Enum + Desc
Structured string shape (date, time, code pattern)	Type only
Values with logical sub-groups (e.g. MIME types by category)	Type with namespace sub-types
Need to map each member to a non-label value	Additional value-mapping dict
Type already exists on a DTO interface	Enum only (skip type file)

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Workflow

1. Identify the concept and its values (or pattern for template literals).
2. Create the type file.
3. Create the enum file (skip for template literals).
4. Create the dict file(s) — clarify with the user what label or mapping is needed if not obvious from context.
5. Add all new files to their respective index.ts barrel.
6. Run typecheck to verify — the Enum<T> and Desc<T> constraints will catch any missing or extra members at compile time.