class WireResponseContext

|WireResponseContext| is used to monitor the outcome of an outstanding asynchronous

|FidlMethod| method call without heap memory allocation. They are used in

combination with the caller-allocating async API flavors of FIDL clients.

## Lifecycle

The FIDL runtime has no requirements on how |WireResponseContext|s are

allocated.

Once a |WireResponseContext| is passed to the client, ownership is

transferred to the FIDL runtime. Ownership is returned back to the user when

|OnResult| is invoked. This means that the user must keep the response

context object alive for the duration of the async method call. |OnResult| is

guaranteed to be invoked exactly once regardless of success or error.

## Usage

Subclass |WireResponseContext| and override its |OnResult| method. Example:

// Lets say we have a `Game` object that loads some required asset

// using the `Disk` FIDL protocol and its `Download` method.

class Game : public fidl::WireResponseContext

<Disk

::Download> {

public:

void LoadGame() {

// Passing `this` to the caller-allocating flavor since `Game`

// implements the corresponding response context.

disk_client_.buffer(arena_)->Download("foo.zip").ThenExactlyOnce(this);

}

private:

void OnResult(fidl::WireUnownedResult

<Disk

::Download>

&

result) final {

if (!result.ok()) {

std::cerr

<

<

"Downloading failed: "

<

<

result.error();

return;

}

// Access the response.

fidl::WireResponse

<Disk

::Download>

&

response = result.value();

}

fidl::WireClient

<Disk

> disk_client_;

fidl::Arena

<

> arena_;

};