# using — Imports and Namespaces (Phase 15)

Status: Accepted (Runner‑side resolution). Selfhost parser accepts using as no‑op and attaches `meta.usings` for future use.

Policy
- Accept `using` lines at the top of the file to declare module namespaces or file imports.
- Resolution is performed by the Rust Runner when `NYASH_ENABLE_USING=1`.
  - Runner strips `using` lines from the source before parsing/execution.
  - Registers modules into an internal registry for path/namespace hints.
- Selfhost compiler (Ny→JSON v0) collects using lines and emits `meta.usings` when present. The bridge currently ignores this meta field.

Syntax
- Namespace: `using core.std` or `using core.std as Std`
- File path: `using "apps/examples/string_p0.nyash" as Strings`
- Relative path is allowed; absolute paths are discouraged.

Style
- Place all `using` lines at the top of the file, before any code.
- One using per line; avoid trailing semicolons. Newline separation is preferred.
- Order: sort alphabetically by target. Group namespaces before file paths.
- Prefer an explicit alias (`as ...`) when the target is long. Suggested alias style is `PascalCase` (e.g., `Std`, `Json`, `UI`).

Examples
```nyash
using core.std as Std
using "apps/examples/string_p0.nyash" as Strings

static box Main {
  main(args) {
    local console = new ConsoleBox()
    console.println("hello")
    return 0
  }
}
```

Runner Configuration
- Enable using pre‑processing: `NYASH_ENABLE_USING=1`
- Selfhost pipeline keeps child stdout quiet and extracts JSON only: `NYASH_JSON_ONLY=1` (set by Runner automatically for child)
- Selfhost emits `meta.usings` automatically when present; no additional flags required.

Notes
- Phase 15 keeps resolution in the Runner to minimize parser complexity. Future phases may leverage `meta.usings` for compiler decisions.
- Unknown fields in the top‑level JSON (like `meta`) are ignored by the current bridge.