[tarantool-patches] Re: [PATCH v1 1/1] Implement mp_stack_top for mp_stack class

[Vladimir Davydov]

On Wed, Apr 03, 2019 at 06:16:25PM +0300, Kirill Shcherbatov wrote:
> > or something like that. BTW, if you agree, let's also rename 'curr' to
> > 'idx' or 'index' - 'curr' looks kinda ugly and since now we are going to
> > access it directly, we'd better rename it IMO.
> > 
> > What do you think?
> 
> I am not shure that it is good concept. Consider a part of MP_PRINT macro
> 
> 	while (!mp_stack_is_empty(&stack)) {
> 		struct mp_frame *frame = mp_stack_top(&stack);
> 		enum mp_type type = frame->type;
> 		bool stop = !mp_frame_advance(frame);
> 		if (frame->idx == 0 || frame->count == 0)
> 			PRINTF(type == MP_ARRAY ? "[" : "{");
> 		if (stop) {
> 			PRINTF(type == MP_ARRAY ? "]" : "}");
> 			mp_stack_pop(&stack);
> 			continue;
> 		} else if (frame->idx != 0) {
> 			PRINTF(type == MP_MAP && frame->idx % 2 == 1 ? ": " : ", ");
> 		}
> 		goto next;
> 	}
> 
> To my opinion, the code got worse.

Yeah, you're right, with the 'stop' flag it doesn't look good.
However, we could rewrite it in a slightly different fashion.
So here's what we have now for comparison:

	while (!mp_stack_is_empty(&stack)) {
		enum mp_type type = mp_stack_type(&stack);
		int curr = mp_stack_advance(&stack);
		if (curr == 0 || mp_stack_count(&stack) == 0)
			PRINTF(type == MP_ARRAY ? "[" : "{");
		if (curr == -1) {
			PRINTF(type == MP_ARRAY ? "]" : "}");
			mp_stack_pop(&stack);
			continue;
		} else if (curr != 0) {
			PRINTF(type == MP_MAP && curr % 2 == 1 ? ": " : ", ");
		}
		goto next;
	}

Here's what we could turn this into using the new API:

	while (!mp_stack_is_empty(&stack)) {
		enum mp_frame *frame = mp_stack_top(&stack);
		if (frame->idx < 0)
			PRINTF(type == MP_ARRAY ? "[" : "{");
		if (!mp_frame_advance(frame)) {
			PRINTF(type == MP_ARRAY ? "]" : "}");
			mp_stack_pop(&stack);
			continue;
		} else if (frame->idx != 0) {
			PRINTF(type == MP_MAP && frame->idx % 2 == 1 ? ": " : ", ");
		}
		goto next;
	}

Now it's not that bad, don't you agree? We even managed to get rid of
the empty array/map check.