kithara-platform 0.0.1-alpha5

/// Wrapper that unconditionally implements `Send` on WASM.
///
/// On native, `WasmSend<T>` is `Send` only if `T: Send` (no magic).
/// On WASM, `WasmSend<T>` is always `Send`, allowing `!Send` types
/// (like `Writer` wrapping a `JsValue`-backed response stream) to be
/// moved into a Web Worker.
///
/// # Safety contract
///
/// The caller must ensure that:
/// - The wrapped value is **not** actively used across threads simultaneously.
/// - When transferring to a Web Worker, any `!Send` JS-backed values inside
///   must be `None`/uninitialized at transfer time and only populated inside
///   the target worker (where JS objects belong to the local context).
///
/// `FileDownloader` satisfies this: `writer` is `None` when moved to the
/// Worker, and `ensure_writer()` creates the HTTP stream inside the Worker.
///
/// The struct and its accessors are cross-platform; the per-target `Send`
/// impl lives in the owning backend (`native`/`wasm` `maybe_send.rs`).
#[derive(fieldwork::Fieldwork)]
#[fieldwork(get)]
pub struct WasmSend<T>(
    #[field(
        get(name = get, doc = "Immutable access."),
        get_mut(name = get_mut, doc = "Mutable access.")
    )]
    T,
);

impl<T> WasmSend<T> {
    /// Wrap a value.
    pub const fn new(value: T) -> Self {
        Self(value)
    }
}