Opaque

A nominal, branded handle to a value the engine owns and manages — a GUI node, a texture, a render target, a physics body, a socket, and so on: hold it and pass it back to the API, but never inspect or construct it. You get one back from an engine function, keep it in a variable, and pass it to the other functions that act on that resource; treat it as an opaque ticket, meaningful to the engine, not a value you read or assemble yourself.

Why a dedicated type? Each kind of handle is its own brand, so the compiler keeps them apart: Opaque<"node"> and Opaque<"texture"> are different types, and passing a texture where a node is expected is a compile error, exactly as a wrong primitive would be. The brand is a phantom unique symbol property that lives only in the type system and is erased at transpile — at runtime the value is just the engine's userdata. Because the symbol is never exported, your code cannot fabricate a handle or inspect or construct one; the engine API is the only source.

The handle kinds modeled today:

• GUI & rendering: Opaque<"node">, Opaque<"texture">, Opaque<"render_target">, Opaque<"constant">, Opaque<"constant_buffer">
• Resources & buffers: Opaque<"resource">, Opaque<"buffer">, Opaque<"bufferstream">
• Sockets: Opaque<"client">, Opaque<"server">, Opaque<"master">, Opaque<"connected">, Opaque<"unconnected">
• Box2D physics: Opaque<"b2Body">, Opaque<"b2World">
• Generic: Opaque<"userdata">

Handles always come back from the engine — for instance:

const node = gui.get_node("button");          // Opaque<"node">
const rt = render.render_target("rt", opts);  // Opaque<"render_target">
const cb = render.constant_buffer();          // Opaque<"constant_buffer">
const buf = resource.load_buffer(path);       // Opaque<"buffer">
const stream = buffer.get_stream(buf, "rgb"); // Opaque<"bufferstream">
const world = b2d.get_world();                // Opaque<"b2World">
const [conn] = socket.tcp();                  // a "master" socket handle
function update(self: ...) {}                 // self is Opaque<"userdata">

Contrast with a LuaTable alias, which says the opposite — "inspect freely, the shape just isn't modeled." An Opaque says "do not look inside; this value is meaningful only to the engine."