[{"_1":2,"_3":-5,"_4":-5},"loaderData",{"_5":6,"_7":8,"_9":10,"_11":12},"actionData","errors","root",{"_164":-5,"_167":168,"_169":170},"routes/shell",{"_41":42,"_163":-5,"_164":-5,"_165":166},"routes/repo",{"_34":-7,"_35":36,"_37":38,"_39":40,"_41":42,"_43":32,"_44":32,"_45":32,"_46":32,"_47":32,"_48":32,"_49":50,"_51":52,"_53":32,"_54":-7,"_55":-7,"_56":57,"_58":59,"_60":61,"_62":-5,"_63":64,"_65":66,"_67":68,"_69":70},"routes/repo.blob",{"_13":14,"_15":16,"_17":18,"_19":20,"_21":22,"_23":24,"_25":-5,"_26":27,"_28":29,"_29":30,"_31":32,"_33":14},"ref","main","path","base/posts/ferrotype.md","oid","dc257e78be07dad75a020e85b07bf986325c1d8c","size",5348,"commit","b9dc342c5ccb4acd3fc070156324fb89e3149117","mounts",[],"source","plain",{"_13":14,"_15":16},"kind","text","---\ntitle: \"Ferrotype\"\ndate: 2026-01-12\n---\n\n# Ferrotype\n\n[Ferrotype](https://github.com/iamnbutler/ferrotype) is a Rust-to-TypeScript type generator. The existing options in this space mostly produce basic, flat types — `Record` everywhere, no discriminated unions, no generics, none of the type-level features that make TypeScript actually good. The generated types compile, technically, but they're not types you'd want to write by hand. Ferrotype tries to close that gap.\n\n```bash\ncargo add ferro-type\n```\n\n## The basics\n\nDerive `TS` on a struct, get a TypeScript type:\n\n```rust\n#[derive(TS)]\n#[ts(rename_all = \"camelCase\")]\nstruct UserProfile {\n display_name: String,\n avatar_url: Option,\n post_count: u32,\n is_verified: bool,\n}\n```\n\n```typescript\ntype UserProfile = {\n displayName: string;\n avatarUrl: string | null;\n postCount: number;\n isVerified: boolean;\n};\n```\n\n`rename_all` respects casing conventions — your Rust stays `snake_case`, your TypeScript gets `camelCase`. `Option` becomes `T | null`, not `T | undefined` or some wrapper type. The basics should just feel right.\n\n## Discriminated unions\n\nThis is where most typegens fall apart. Rust enums are sum types — they should generate proper discriminated unions, not `string | object` or some untyped mess.\n\n```rust\n#[derive(TS)]\n#[ts(tag = \"kind\")]\nenum ApiResponse {\n Loading,\n Success { data: Vec, total: u32 },\n Error { code: i32, message: String },\n}\n```\n\n```typescript\ntype ApiResponse =\n | { kind: \"Loading\" }\n | { kind: \"Success\"; data: Post[]; total: number }\n | { kind: \"Error\"; code: number; message: string };\n```\n\nTypeScript narrows these automatically in `switch` statements and `if` checks. The `tag` attribute controls the discriminant field name — default is `type`, but `kind`, `variant`, whatever you want.\n\nFor adjacently tagged enums (serde's `tag` + `content` style):\n\n```rust\n#[derive(TS)]\n#[ts(tag = \"type\", content = \"data\")]\nenum Event {\n Click { x: f64, y: f64 },\n Keypress(String),\n Blur,\n}\n```\n\n```typescript\ntype Event =\n | { type: \"Click\"; data: { x: number; y: number } }\n | { type: \"Keypress\"; data: string }\n | { type: \"Blur\" };\n```\n\nUntagged unions work too — `#[ts(untagged)]` gives you a plain `A | B | C` union.\n\n## Generics\n\nGeneric structs produce generic types:\n\n```rust\n#[derive(TS)]\n#[ts(rename_all = \"camelCase\")]\nstruct Paginated {\n items: Vec,\n total_count: u32,\n has_next_page: bool,\n}\n```\n\n```typescript\ntype Paginated = {\n items: T[];\n totalCount: number;\n hasNextPage: boolean;\n};\n```\n\nSo `Paginated` in Rust gives you `Paginated` in TypeScript. The generic constraint carries through — you don't lose the relationship between the two sides.\n\n## Composition and extension\n\n`flatten` inlines fields from a nested struct, the same way serde does:\n\n```rust\n#[derive(TS)]\nstruct Timestamps {\n created_at: String,\n updated_at: String,\n}\n\n#[derive(TS)]\nstruct Post {\n title: String,\n #[ts(flatten)]\n timestamps: Timestamps,\n}\n```\n\n```typescript\ntype Post = {\n title: string;\n createdAt: string;\n updatedAt: string;\n};\n```\n\nFor extending external types you don't control, `extends` generates intersection types:\n\n```rust\n#[derive(TS)]\n#[ts(extends = \"BaseEntity\")]\nstruct User {\n name: String,\n email: String,\n}\n```\n\n```typescript\ntype User = BaseEntity & { name: string; email: string };\n```\n\n## Template literals and branded types\n\nThis is the kind of thing no other typegen even attempts. TypeScript has template literal types — ferrotype can generate them:\n\n```rust\n#[derive(TS)]\nstruct Order {\n #[ts(pattern = \"order-${string}\")]\n id: String,\n #[ts(pattern = \"${number}px\")]\n width: String,\n}\n```\n\n```typescript\ntype Order = {\n id: `order-${string}`;\n width: `${number}px`;\n};\n```\n\nNow your TypeScript compiler rejects `\"abc123\"` as an order ID but accepts `\"order-abc123\"`. The type system does the validation.\n\n## Indexed access types\n\nReference a field's type from another type, keeping them in sync:\n\n```rust\n#[derive(TS)]\nstruct Comment {\n #[ts(index = \"User\", key = \"id\")]\n author_id: String,\n body: String,\n}\n```\n\n```typescript\ntype Comment = {\n authorId: User[\"id\"];\n body: string;\n};\n```\n\nIf `User[\"id\"]` changes from `string` to `number`, every type referencing it updates automatically. No manual syncing.\n\n## The registry\n\nTypes aren't generated in isolation. `TypeRegistry` collects everything, deduplicates, and renders in dependency order:\n\n```rust\nlet mut registry = TypeRegistry::new();\nregistry.register::(); // pulls in Post, User, etc.\nlet output = registry.render();\n```\n\nIf `ApiResponse` references `Post` which references `User`, all three get emitted in the right order. No forward reference issues, no duplicates.\n\n## Everything else\n\nA few more things that matter for real-world usage: `#[ts(skip)]` omits fields, `#[ts(default)]` marks fields optional (`?`), `#[ts(type = \"Date\")]` overrides the generated type when you need an escape hatch, `#[ts(inline)]` inlines a type definition instead of emitting a reference, and `#[ts(transparent)]` on a newtype wrapper dissolves it into its inner type.\n\nNamed it after the [tintype photography process](https://en.wikipedia.org/wiki/Tintype) — ferro for iron/Rust, type for types.\n","editable",false,"branch","documentNavigation","repo","iamnbutler/stylize","repoId","8871e6fb-e95a-4af9-989d-99d4aa74240b","ownerId","user:1714999","site","nexthub","private","admin","settings","maintainer","triage","starred","stars",0,"watchers",1,"watching","pinned","notify","views",[119,120,121,122,123,124,125,126,127,128,129,130,131],"navigation",{"_56":57,"_79":80,"_81":82,"_83":84,"_85":86,"_87":88,"_89":90},"sources",[],"viewer","meta",{"_71":72,"_73":74,"_75":76,"_43":32,"_77":14,"_78":32,"_49":50,"_51":52},"branches",[14],"tags",[],"cloneUrl","https://git.nexthub.sh/iamnbutler/stylize.git","description","One design prompt, many agents: opus-5-5 redesigns a blog from visual inspo. Live demos at demos.githubnext.com/iamnbutler/stylize","owner","iamnbutler","section","","head","empty","pins",[101,102,103],"documents",{"_98":99,"_100":50},"code",{"_95":96,"_97":50},"automations",{"_93":50,"_94":-5},"delivery",{"_91":50,"_92":-5},"tag","7cQwjAtDu_65xzj3DIEQPJBEoJf","releases","applications","workflows","deployments","commits",3,"changes","counts",{},"total",{"_104":97,"_106":117,"_15":97,"_108":118,"_54":110,"_111":32,"_112":110,"_113":50},{"_104":114,"_106":115,"_15":114,"_108":116,"_54":110,"_111":32,"_112":110,"_113":50},{"_104":105,"_106":107,"_15":105,"_108":109,"_54":110,"_111":32,"_112":110,"_113":50},"id","issues","name","Issues","filters",{},true,"saved","pinnable","count","tasks","Tasks",{},"Changes",{},{"_104":97,"_106":117,"_15":97,"_108":162,"_54":110,"_111":32,"_112":110},{"_104":114,"_106":115,"_15":114,"_108":161,"_54":110,"_111":32,"_112":110},{"_104":105,"_106":107,"_15":105,"_108":160,"_54":110,"_111":32,"_112":110},{"_104":157,"_106":158,"_15":157,"_108":159,"_54":32,"_111":32,"_112":110},{"_104":154,"_106":155,"_15":154,"_108":156,"_54":32,"_111":32,"_112":110},{"_104":93,"_106":152,"_15":85,"_108":153,"_54":32,"_111":32,"_112":110},{"_104":94,"_106":149,"_15":150,"_108":151,"_54":32,"_111":32,"_112":110},{"_104":91,"_106":147,"_15":91,"_108":148,"_54":32,"_111":32,"_112":110},{"_104":143,"_106":144,"_15":145,"_108":146,"_54":32,"_111":32,"_112":110},{"_104":81,"_106":141,"_15":81,"_108":142,"_54":32,"_111":32,"_112":32},{"_104":138,"_106":139,"_15":138,"_108":140,"_54":32,"_111":32,"_112":32},{"_104":135,"_106":136,"_15":135,"_108":137,"_54":32,"_111":32,"_112":32},{"_104":132,"_106":133,"_15":132,"_108":134,"_54":32,"_111":32,"_112":32},"decisions","Decisions",{},"changelog","Changelog",{},"roadmap","Roadmap",{},"Documents",{},"activity","Activity","insights",{},"Releases",{},"Deployments","automations/deployments",{},"Workflows",{},"discussions","Discussions",{},"goals","Goals",{},{},{},{},"groups","user","agents",[],"now",1794435196080,"sidebar","expanded"]