Pine var and varip in MQL5: values that persist between bars

//@version=6
indicator("var and varip", overlay = false)

// var: initialized once, on the first bar, then keeps its value from bar to bar
var int upBars = 0
if close > open
    upBars += 1

// var with a reset: the day's high so far
var float dayHigh = na
if timeframe.change("D") or na(dayHigh)
    dayHigh := high
else
    dayHigh := math.max(dayHigh, high)

// varip: also keeps what each real-time tick changed (no rollback between ticks)
varip int ticks = 0
if barstate.isrealtime
    ticks += 1

plot(upBars, "Up bars so far", color.teal, 2)
plot(dayHigh, "Day high so far", color.orange, display = display.data_window)
plot(ticks, "Real-time ticks seen", color.gray, display = display.data_window)

//+------------------------------------------------------------------+
//| var and varip in MQL5                                            |
//| var   -> a value carried from the previous bar's buffer element  |
//| varip -> a global variable changed on every tick                 |
//| Custom indicator: save in MQL5/Indicators and compile (F7).      |
//+------------------------------------------------------------------+
#property indicator_separate_window
#property indicator_buffers 3
#property indicator_plots   3

#property indicator_label1  "Up bars so far"
#property indicator_type1   DRAW_LINE
#property indicator_color1  clrTeal
#property indicator_width1  2
#property indicator_label2  "Day high so far"
#property indicator_type2   DRAW_NONE
#property indicator_label3  "Real-time ticks seen"
#property indicator_type3   DRAW_NONE

double UpBarsBuf[], DayHighBuf[], TicksBuf[];

// varip int ticks = 0: a global survives from one tick to the next, and nothing rolls it back
int ticks = 0;

int OnInit()
  {
   SetIndexBuffer(0, UpBarsBuf, INDICATOR_DATA);
   SetIndexBuffer(1, DayHighBuf, INDICATOR_DATA);
   SetIndexBuffer(2, TicksBuf, INDICATOR_DATA);
   PlotIndexSetDouble(2, PLOT_EMPTY_VALUE, EMPTY_VALUE);
   ticks = 0;  // reset here too: an Expert Advisor keeps its globals when only the symbol or timeframe changes
   return INIT_SUCCEEDED;
  }

// True if the two times fall on different days (server time)
bool NewDay(const datetime prev, const datetime cur)
  {
   MqlDateTime a, b;
   TimeToStruct(prev, a);
   TimeToStruct(cur, b);
   return a.day != b.day || a.mon != b.mon || a.year != b.year;
  }

int OnCalculate(const int rates_total,
                const int prev_calculated,
                const datetime &time[],
                const double &open[],
                const double &high[],
                const double &low[],
                const double &close[],
                const long &tick_volume[],
                const long &volume[],
                const int &spread[])
  {
   int start = prev_calculated > 0 ? prev_calculated - 1 : 0;
   for(int i = start; i < rates_total; i++)
     {
      // var int upBars = 0 / if close > open: upBars += 1
      // Built from the PREVIOUS bar's value, so recalculating the forming bar on every tick
      // never counts it twice: that is Pine's rollback of var on real-time ticks
      double before = i > 0 ? UpBarsBuf[i - 1] : 0.0;
      UpBarsBuf[i] = before + (close[i] > open[i] ? 1.0 : 0.0);

      // var float dayHigh = na, reset on a new day
      if(i == 0 || NewDay(time[i - 1], time[i]))
         DayHighBuf[i] = high[i];
      else
         DayHighBuf[i] = MathMax(DayHighBuf[i - 1], high[i]);

      TicksBuf[i] = EMPTY_VALUE;
     }

   // varip: counts every real-time call (prev_calculated > 0 once the history has been calculated)
   if(prev_calculated > 0)
      ticks++;
   TicksBuf[rates_total - 1] = ticks;
   return rates_total;
  }
//+------------------------------------------------------------------+