thinkscript if function useless in important case

问题

The thinkscript if function fails to branch as expected in an important case. The following test case can be used to reproduce this severe bug / defect.

In a nutshell, an if statement may normally be used to prevent a function call from being executed if one of its function parameters is invalid. We show that this is not the case. In fact, both branches are executed, including the branch not meeting the if condition.

This absolutely defeats the purpose of the test of the if condition, the test that every if statement in every language has.

Following is some sample code that shows the problem on a chart. The result can be seen by clicking on the "i" message icon blinking in the left top corner of the chart:

Folding: 'from' cannot be greater than 'to': 1 > -1.

# Get the current offset from the right edge from BarNumber()
# BarNumber(): The current bar number. On a chart, we can see that the number increases
# from left 1 to number of bars e.g. 140 at the right edge.
def barNumber = BarNumber();
def barCount = HighestAll(barNumber);
# rightOffset: 0 at the right edge, i.e. at the rightmost bar,
# increasing from right to left.
def rightOffset = barCount - barNumber;

# This script gets the minimum value from data in the offset range between startIndex
# and endIndex. It serves as a functional but not direct replacement for the
# GetMinValueOffset function where a dynamic range is required. Expect it to be slow.
script getMinValueBetween {
    input data = low;
    input startIndex = 0;
    input endIndex = 0;
    plot minValue = fold index = startIndex to endIndex with minRunning = Double.POSITIVE_INFINITY do Min(GetValue(data, index), minRunning);
}

# Call this only once at the last bar.
script buildConditions {
    input startIndex = 1;
    input endIndex = -1;
# Since endIndex < startIndex, getMinValueBetween() should never
# be executed. However it is executed nevertheless.
    plot minValue = if (endIndex > startIndex) then getMinValueBetween(low, startIndex, endIndex) else close[startIndex];
}
plot scan;
if (rightOffset == 0) {
    scan = buildConditions();
} else {
    scan = 0;
}
declare lower;

回答1:

The question has the answer in its first sentence.

One might contemplate using the if statement (vs the if function). However, that is broken as demonstrated in

thinkscript if statement failure

来源：https://stackoverflow.com/questions/58354407/thinkscript-if-function-useless-in-important-case

标签

thinkscript