examples/research_projects/visual_bert/modeling_frcnn.py/GeneralizedRCNN/__init__
class GeneralizedRCNN:    def __init__(self, cfg):
        super().__init__()

        self.device = torch.device(cfg.MODEL.DEVICE)
        self.backbone = build_backbone(cfg)
        self.proposal_generator = RPN(cfg, self.backbone.output_shape())
        self.roi_heads = Res5ROIHeads(cfg, self.backbone.output_shape())
        self.roi_outputs = ROIOutputs(cfg)
        self.to(self.device)