SampleTodo

SampleTodo

A minimal C# todo-list library that demonstrates the basic building blocks of Metano: records, string enums, method transpilation, LINQ, and method overloads.

This is the best starting point to see what Metano produces from a small, simple domain model.

What this sample demonstrates

Feature	C#	Generated TS
String enum	[StringEnum] public enum Priority { Low, Medium, High }	const Priority = { Low: "low", Medium: "medium", High: "high" } as const
[Name("x")] override	[Name("low")] Low	Value "low" instead of "Low"
Record with defaults	public record TodoItem(string Title, bool Completed = false, Priority Priority = Priority.Medium)	Class with equals, hashCode, with, default values
with expression	this with { Completed = !Completed }	this.with({ completed: !this.completed })
override ToString()	public override string ToString() => $"[{...}] {Title}"	toString() method with template literal
Primary constructor class	public class TodoList(string name)	Class with name field from constructor
IReadOnlyList<T>	public IReadOnlyList<TodoItem> Items => _items	Iterable<TodoItem> getter
LINQ queries	_items.Count(i => !i.Completed)	.filter(i => !i.completed).length
Method overloads	Add(TodoItem), Add(string), Add(string, Priority)	Single method with runtime dispatcher + private fast-path methods
Nullable return	TodoItem? FindByTitle(...)	TodoItem | null return type
JsonSerializerContext	[JsonSerializable(typeof(TodoItem))] class JsonContext : JsonSerializerContext	JsonContext extends SerializerContext with lazy TypeSpec getters

Files

• AssemblyInfo.cs — Marks the assembly with [TranspileAssembly] and [EmitPackage("sample-todo")] so consumers can import { TodoItem } from "sample-todo".
• Priority.cs — String enum with [Name("x")] overrides for wire format.
• TodoItem.cs — Record with methods and ToString() override.
• TodoList.cs — Primary constructor class with private state, computed properties, LINQ queries, and method overloads.
• JsonContext.cs — JSON serializer context (transpiles to TypeScript SerializerContext).

Generated output

The transpiled TypeScript lives in ../../targets/js/sample-todo/src. Key files:

• priority.ts — the string union type
• todo-item.ts — the class with equals, hashCode, with
• todo-list.ts — the class with the overloaded add method + dispatcher
• json-context.ts — the serializer context
• index.ts — barrel file re-exporting everything

The generated package.json has "name": "sample-todo" and is consumed by SampleTodo.Service via a cross-package import.

How to build

From the repository root:

# Build the C# project (auto-transpiles via Metano.Build integration)
dotnet build samples/SampleTodo/SampleTodo.csproj

# Or build everything
dotnet build

How to test the generated code

cd targets/js/sample-todo
bun install
bun run build
bun test

You should see 18 tests passing, covering:

• Record equality and hashCode
• The with expression creating copies
• toggleCompleted() and setPriority() returning new instances
• toString() formatting
• TodoList.add() overload dispatch
• findByTitle() returning null for missing items
• LINQ-based pendingCount and hasPending()
• String enum value checks