MQL5 traps

Index direction#

In MQL5 a series array is often read newest first, so index 0 is the current bar. A port that keeps close[1] for "the previous bar" reads the wrong bar.

import forge as fg

FORGE_API = 1


def last_two_closes(close):
    # Oldest first: [-1] is the latest closed bar, [-2] the one before it.
    return close[-2], close[-1]

Point, Digits and pips#

_Point is the smallest price step and _Digits its number of decimals. A pip is 10 points on symbols with 5 or 3 digits and 1 point elsewhere. Forge prices are raw prices such as 1.08543, never points or pips. A pip or point amount appears only where a price amount is typed, and is resolved through the broker facts.

EMPTY_VALUE#

An indicator buffer holds EMPTY_VALUE for "no value", which is a very large number. Forge uses NaN, and a comparison with NaN is false.

import forge as fg
from forge import ta

FORGE_API = 1


def ready(value):
    # A missing value is NaN, never a sentinel number.
    return ~ta.isna(value)

Hedging and netting#

An MQL5 account is either hedging, which allows several positions on one symbol, or netting, which keeps one. Forge reads the account's margin mode from the broker facts. A strategy that opens an opposite order on a netting account reduces or reverses the position, and an order the account does not allow is rejected with a named reason.

Ticks and bars#

An expert advisor reacts in OnTick, on every price update. A Forge strategy decides on closed bars and fills at the next real price. A port that depended on the tick it was called on needs another design, or a bar type built from ticks.

Magic numbers#

A magic number tags the orders of one expert advisor. Forge orders carry a tag, and a strategy lists its own positions by tag.

prev_calculated#

OnCalculate receives prev_calculated, the number of bars already done. Forge passes start, the first bar to fill, to calculate. Fill every output from start on and do not keep your own count.