:title
ONCE

:sig
ONCE(Request& context)

:see
>1_COMPONENT
>1_INIT
>1_RENDER
>1_WS
>3_C++ Preprocessor
>unit_call

:content
Defines a request-local one-time hook for the current `.uce` unit.

When a request first enters a given file through `RENDER(Request& context)`, `COMPONENT(Request& context)`, or any `COMPONENT:NAME(Request& context)` handler, the runtime checks whether that unit exposes `ONCE(Request& context)`. If it does, the hook runs before the selected render or component handler.

`ONCE()` is tracked per request and per resolved unit file, so repeated component calls to the same file inside one request do not rerun it.

## Typical Uses

- prepare request-local derived state on `context.call`
- load request-scoped config or data needed by multiple named component handlers
- normalize shared props before the unit's first render/component call

## Example

```cpp
ONCE(Request& context)
{
	context.call["card_defaults"]["tone"] = "info";
}

COMPONENT(Request& context)
{
	<>
		<div class="card card-<?= context.call["card_defaults"]["tone"] ?>">
			<?: component(":BODY", context.props, context) ?>
		</div>
	</>
}
```

## Related Concepts

- PHP: per-request bootstrap work before a template or partial first runs
- JavaScript / Node.js: request-scoped lazy initialization before a route or component render