yIdDirectPrivate(reader, "closedPromiseCapability", @newPromiseCapability(@Promise));
    else if (@getByIdDirectPrivate(stream, "state") === @streamClosed)
        @putByIdDirectPrivate(reader, "closedPromiseCapability", { @promise: @Promise.@resolve() });
    else {
        @assert(@getByIdDirectPrivate(stream, "state") === @streamErrored);
        @putByIdDirectPrivate(reader, "closedPromiseCapability", { @promise: @newHandledRejectedPromise(@getByIdDirectPrivate(stream, "storedError")) });
    }
})