![\"Combined](\"https:\/\/ruby-doc.org\/learn\/wp-content\/uploads\/2026\/09\/combined-ruby-swift-programming-tutorial-code-featured.webp\")
What the Ruby and Swift programs will share<\/h2>\n\n\n\n
Our example exports a short reading list. Each item has a text name and a whole-number quantity. The top-level object also has a schema version. That version describes the file format agreed by these two programs; it is unrelated to the installed Ruby or Swift version.<\/p>\n\n\n\n
The contract accepts at most 1,000 items, with quantities from 0 to 10,000. Those modest limits keep the demonstration’s total within a comfortable range. The consumer checks them after decoding. A valid JSON document is not automatically valid application data.<\/p>\n\n\n\n
Use a fresh working folder with Ruby and a Swift toolchain installed. Confirm that Save the following as Ruby’s JSON reference documents the conversion<\/a> of hashes and arrays with Do not replace the generator with Run Save this code as Apple’s guide to encoding and decoding custom types<\/a> explains the protocol-based approach. This program only reads data, so its structures adopt First, the decoder checks the required fields and their types. The guards then check application rules: a supported schema, a bounded list, a non-blank name and an allowed quantity. These are separate stages. For example, a negative integer can decode successfully but fail the quantity rule.<\/p>\n\n\n\n The error handler reports failures in one place and exits with a nonzero status. That lets a shell or a later automation job tell success from failure. The diagnostic is useful for this exercise; a user-facing application would usually translate it into a clearer message.<\/p>\n\n\n\n The examples passed end-to-end checks with Ruby 3.2.3 and Swift 6.2.1 on Linux, including the compiled and script forms of the importer. From the folder containing both source files, run these commands in order. The first creates the input consumed by the second.<\/p>\n\n\n\n The exporter prints Run the importer again without changing If you prefer a compiled executable, run Change a copy of The value has become JSON text instead of a number. Decoding into Int fails. Keep the producer and consumer agreement explicit; do not silently convert every unexpected type just to make the import continue.<\/p>\n<\/details>\n\n\n\n The data can decode, but the version guard rejects it. A future format needs a deliberate migration or a consumer that understands both versions. Changing the number alone does not add compatibility.<\/p>\n<\/details>\n\n\n\n A missing file fails during the read. A blank name reaches the application validation and fails there. In both cases the program reports an import failure and returns a nonzero exit status.<\/p>\n<\/details>\n\n\n\n Try an empty items array next. It is valid under this contract and produces For more Ruby practice, use our Ruby code examples<\/a>. If the exporter needs to filter or transform a collection, our functional programming guide<\/a> can help you keep that work understandable.<\/p>\n\n\n\n This small reader loads the whole file into memory. Its item limit applies after decoding, so it is not a pre-read file-size limit. For large or untrusted files, add appropriate size controls and consider a different ingestion design. When moving to HTTP, also define timeouts, authentication and retry behaviour.<\/p>\n\n\n\n Keep JSON as data. Neither program needs Build two small programs with one clear contract: Ruby exports a reading list and Swift decodes, validates and totals it.<\/p>\n","protected":false},"author":3,"featured_media":1610,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3],"tags":[],"class_list":["post-1616","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-ruby-tips"],"blocksy_meta":{"styles_descriptor":{"styles":{"desktop":"","tablet":"","mobile":""},"google_fonts":[],"version":7}},"yoast_head":"\nruby --version<\/code> and swift --version<\/code> work in your terminal. The tutorial uses Foundation in Swift and Ruby’s JSON library. It needs no Rails app, package dependency or running web server.<\/p>\n\n\n\nStep 1: write the Ruby exporter<\/h2>\n\n\n\n
export.rb<\/code>. It writes catalog.json<\/code> in the current working directory, replacing a file with that name if one already exists. Use the fresh tutorial folder so the output has a clear owner.<\/p>\n\n\n\nrequire \"json\"\n\ncatalog = {\n \"schema_version\" => 1,\n \"items\" => [\n { \"name\" => \"Ruby guide\", \"quantity\" => 2 },\n { \"name\" => \"Swift notes\", \"quantity\" => 1 }\n ]\n}\n\nFile.write(\"catalog.json\", JSON.generate(catalog) + \"\\n\")\nputs \"Wrote catalog.json\"<\/code><\/pre>\n\n\n\nJSON.generate<\/code>. The result is a string containing JSON. File.write<\/code> then writes that string to disk.<\/p>\n\n\n\ncatalog.to_s<\/code>. A Ruby object’s diagnostic representation is not the data format promised to the Swift reader. A serializer also handles escaping characters inside strings, so you should not assemble JSON by joining fragments of user text.<\/p>\n\n\n\nruby export.rb<\/code>. After the confirmation message, open the generated file in a text editor. You should see the two named items and a numeric schema version. The file may be compact; whitespace is not what makes the data valid.<\/p>\n\n\n\nStep 2: write the Swift importer<\/h2>\n\n\n\n
import.swift<\/code> in the same folder. The CodingKeys<\/code> enumeration maps Ruby’s JSON key schema_version<\/code> to the Swift property schemaVersion<\/code>. The two names can differ because the mapping is explicit.<\/p>\n\n\n\nimport Foundation\n\nstruct Item: Decodable {\n let name: String\n let quantity: Int\n}\n\nstruct Catalog: Decodable {\n let schemaVersion: Int\n let items: [Item]\n\n enum CodingKeys: String, CodingKey {\n case schemaVersion = \"schema_version\"\n case items\n }\n}\n\nenum CatalogError: Error {\n case unsupportedVersion\n case tooManyItems\n case invalidItem\n}\n\nfunc readCatalog(from path: String) throws -> Catalog {\n let data = try Data(contentsOf: URL(fileURLWithPath: path))\n let catalog = try JSONDecoder().decode(Catalog.self, from: data)\n\n guard catalog.schemaVersion == 1 else {\n throw CatalogError.unsupportedVersion\n }\n guard catalog.items.count <= 1_000 else {\n throw CatalogError.tooManyItems\n }\n guard catalog.items.allSatisfy({ item in\n !item.name.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty\n && (0...10_000).contains(item.quantity)\n }) else {\n throw CatalogError.invalidItem\n }\n return catalog\n}\n\nlet path = CommandLine.arguments.dropFirst().first ?? \"catalog.json\"\n\ndo {\n let catalog = try readCatalog(from: path)\n for item in catalog.items {\n print(\"\\(item.name): \\(item.quantity)\")\n }\n let total = catalog.items.reduce(0) { $0 + $1.quantity }\n print(\"Total copies: \\(total)\")\n} catch {\n FileHandle.standardError.write(Data(\"Import failed: \\(error)\\n\".utf8))\n exit(1)\n}<\/code><\/pre>\n\n\n\nDecodable<\/code>. You would use Codable<\/code> when the same type needs both encoding and decoding support.<\/p>\n\n\n\nStep 3: run the combined Ruby Swift programming tutorial code<\/h2>\n\n\n\n
ruby export.rb\nswift import.swift catalog.json<\/code><\/pre>\n\n\n\nWrote catalog.json<\/code>. The importer should then print:<\/p>\n\n\n\nRuby guide: 2\nSwift notes: 1\nTotal copies: 3<\/code><\/pre>\n\n\n\ncatalog.json<\/code>. It should produce exactly the same result. That repeatability helps with debugging: a fixed file lets you test the consumer independently of the producer.<\/p>\n\n\n\nswiftc import.swift -o catalog-import<\/code>, followed by .\/catalog-import catalog.json<\/code> on macOS or Linux. Both the interpreted command and the compiled program use the same source and contract.<\/p>\n\n\n\nBreak the contract and diagnose the result<\/h2>\n\n\n\n
catalog.json<\/code> so that it breaks one part of the contract, then pass that file’s path to the importer. Predict which stage will reject it before opening the answer.<\/p>\n\n\n\nChange a quantity from 2 to “2”<\/summary>\n
Change schema_version from 1 to 2<\/summary>\n
Remove the file or make an item name blank<\/summary>\n
Extend the example without hiding its boundaries<\/h2>\n\n\n\n
Total copies: 0<\/code>. By contrast, a missing items<\/code> key is an error. An empty collection and absent required data are different states.<\/p>\n\n\n\neval<\/code>, executable content or a shared runtime. Sample files, a written schema and tests for rejected inputs make the agreement between the two languages easier to maintain.<\/p>\n","protected":false},"excerpt":{"rendered":"