fluidly building a signal guard

SignalGuard

package bbc.core.guard
{
public class SignalGuard
{
    public function fire(signal:ISignal):SignalGuard
    {
        _destination = signal

        return build()
    }

    public function when(signal:ISignal):SignalGuard
    {
        _origin = signal

        return build()
    }

    public function unless(guard:Function):SignalGuard
    {
        _guard = guard

        return build()
    }

    private function build():SignalGuard
    {
        if(_origin && _destination && _guard)
        {
            addGuardedSignal(_origin, _destination, _guard)

            _origin = _destination = _guard = null
            return null
        }

        return this
    }
}
}