[{"_1":2,"_3":-5,"_4":-5},"loaderData",{"_5":6,"_7":8,"_9":10,"_11":12},"actionData","errors","root",{"_223":-5,"_226":227,"_228":229},"routes/shell",{"_41":42,"_222":-5,"_223":-5,"_224":225},"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","scripts/posts/ferrotype.md","oid","8b66740812cd610f011be740a8169c2d9194a81c","size",5303,"commit","40184b7743bfad334a49c6ee41d61570eee78057","mounts",[],"source","plain",{"_13":14,"_15":16},"kind","text","# 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/iamnbutler.github.io","repoId","077a62f3-be49-4ad9-923b-62e0436d739f","ownerId","user:1714999","site","nexthub","private","admin","settings","maintainer","triage","starred","stars",0,"watchers",1,"watching","pinned","notify","views",[178,179,180,181,182,183,184,185,186,187,188,189,190],"navigation",{"_56":57,"_136":137,"_138":139,"_140":141,"_142":143,"_144":145,"_146":147},"sources",[],"viewer","meta",{"_128":129,"_130":131,"_132":133,"_43":32,"_134":14,"_135":32,"_49":50,"_51":52},"branches",[73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,14,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127],"tags",[71,72],"cloneUrl","https://git.nexthub.sh/iamnbutler/iamnbutler.github.io.git","v18.0.0","v19.0.0","14-2","2017.3","add-gpui-extended-context-post","add-post-tags","backblaze-assets","dependabot/npm_and_yarn/defu-6.1.6","dependabot/npm_and_yarn/devalue-5.8.1","dependabot/npm_and_yarn/h3-1.15.10","dependabot/npm_and_yarn/multi-04ca55b44c","dependabot/npm_and_yarn/picomatch-2.3.2","dependabot/npm_and_yarn/postcss-8.5.14","dependabot/npm_and_yarn/rollup-4.59.0","dependabot/npm_and_yarn/smol-toml-1.6.1","dependabot/npm_and_yarn/svelte-5.55.7","dependabot/npm_and_yarn/svgo-4.0.1","dependabot/npm_and_yarn/vite-6.4.2","fix-backblaze-integration","fix-backblaze-issue-take2","glfs-test","global-tags","gpui-ui-post","import-and-sort","integrate-data-repo","lists","mellow-fjord/site-reliability-cleanup","nate-journal","revert-34-fix-backblaze-integration","tiny-search-2","unified-feed","update-nuxt","v-11","v-12","v-13","v-14","v-15","v-16","v-18","v-19","v-20","v-21","v-3","v-4","v11-newsprint","v14-1","v14-effect","v18","v19/add-mh-2","v21","v23","v5-04-21-06","v5-static","v8","v8_js","v9","v9-2020-eleventy","description","Personal Site","owner","iamnbutler","section","","head","empty","pins",[160,161,162],"documents",{"_157":158,"_159":50},"code",{"_153":154,"_155":156},"automations",{"_150":151,"_152":-5},"delivery",{"_148":50,"_149":-5},"tag","ckQnXds0_OG2x4LL3veMKJ2xpXN","releases","applications","workflows",2,"deployments","commits",822,"changes",11,"counts",{},"total",{"_163":155,"_165":176,"_15":155,"_167":177,"_54":169,"_170":32,"_171":169,"_172":156},{"_163":173,"_165":174,"_15":173,"_167":175,"_54":169,"_170":32,"_171":169,"_172":50},{"_163":164,"_165":166,"_15":164,"_167":168,"_54":169,"_170":32,"_171":169,"_172":50},"id","issues","name","Issues","filters",{},true,"saved","pinnable","count","tasks","Tasks",{},"Changes",{},{"_163":155,"_165":176,"_15":155,"_167":221,"_54":169,"_170":32,"_171":169},{"_163":173,"_165":174,"_15":173,"_167":220,"_54":169,"_170":32,"_171":169},{"_163":164,"_165":166,"_15":164,"_167":219,"_54":169,"_170":32,"_171":169},{"_163":216,"_165":217,"_15":216,"_167":218,"_54":32,"_170":32,"_171":169},{"_163":213,"_165":214,"_15":213,"_167":215,"_54":32,"_170":32,"_171":169},{"_163":150,"_165":211,"_15":142,"_167":212,"_54":32,"_170":32,"_171":169},{"_163":152,"_165":208,"_15":209,"_167":210,"_54":32,"_170":32,"_171":169},{"_163":148,"_165":206,"_15":148,"_167":207,"_54":32,"_170":32,"_171":169},{"_163":202,"_165":203,"_15":204,"_167":205,"_54":32,"_170":32,"_171":169},{"_163":138,"_165":200,"_15":138,"_167":201,"_54":32,"_170":32,"_171":32},{"_163":197,"_165":198,"_15":197,"_167":199,"_54":32,"_170":32,"_171":32},{"_163":194,"_165":195,"_15":194,"_167":196,"_54":32,"_170":32,"_171":32},{"_163":191,"_165":192,"_15":191,"_167":193,"_54":32,"_170":32,"_171":32},"decisions","Decisions",{},"changelog","Changelog",{},"roadmap","Roadmap",{},"Documents",{},"activity","Activity","insights",{},"Releases",{},"Deployments","automations/deployments",{},"Workflows",{},"discussions","Discussions",{},"goals","Goals",{},{},{},{},"groups","user","agents",[],"now",1794435042926,"sidebar","expanded"]