Strings parameters fail count check when EvaluateOptions.IterateParameters is used

[AzGhort]

Hi,
when implenting custom string functions for NCalc, we discovered a bug which prevents using FunctionArgs.Parameters[N].Evaluate() along with EvaluateOptions.IterateParamers when evaluating parameters in custom function evaluators.

Evaluated string parametes are treated as IEnumerable, and therefore fail the same count check in Expression, see:

ncalc/src/NCalc/Expression.cs

Line 284 in 358ed95

throw new EvaluationException("When IterateParameters option is used, IEnumerable parameters must have the same number of items");

Minimal code to reproduce:

    [Fact]
    public void EndsWith_Test()
    {
        var a = new Expression("EndsWith([x], [y])", EvaluateOptions.IterateParameters);
        a.Parameters["x"] = new[] { "'abc'", "'def'" };
        a.Parameters["y"] = new[] { "'c'", "'c'" };
        a.EvaluateFunction += EndsWith;

        var result = a.Evaluate();
    }

    private static void EndsWith(string name, FunctionArgs args)
    {
        if (name == "EndsWith")
        {
            var firstParam = args.Parameters[0].Evaluate();
            var secondParam = args.Parameters[1].Evaluate();

            if (firstParam is not string firstArg || secondParam is not string secondArg)
            {
                throw new FormatException();
            }

            args.Result = firstArg.StartsWith(secondArg, StringComparison.InvariantCulture);
        }
    }

Version: NCalcSync 3.8.0

[AlPecin]

Hi,
I'm looking for your problem, I think the exception is the result of a recursion to the Iterate loop in the Expression.cs. I suggest the following changes:

Add the marked line to this method in FuntionArgs.cs

public object[] EvaluateParameters()
{
    var values = new object[_parameters.Length];
    for (var i = 0; i < values.Length; i++)
    {
        parameters[i].Options &= ~EvaluateOptions.IterateParameters;  //<- add this line
        values[i] = _parameters[i].Evaluate();
    }

    return values;
}

``
and change your code to this:

        private static void EndsWith(string name, FunctionArgs args)
        {
            if (name == "EndsWith")
            {
                var parameters = args.EvaluateParameters();

                var firstParam = parameters[0];
                var secondParam = parameters[1];

                if (firstParam is not string firstArg || secondParam is not string secondArg)
                {
                    throw new FormatException();
                }

                args.Result = firstArg.EndsWith(secondArg, StringComparison.InvariantCulture);
            }
        }

Without change in ncalc you can do this

    private static void EndsWith(string name, FunctionArgs args)
    {
        if (name == "EndsWith")
        {
            foreach (var parameterExpression in args.Parameters)
                parameterExpression.Options &= ~EvaluateOptions.IterateParameters;

            var firstParam = args.Parameters[0].Evaluate();
            var secondParam = args.Parameters[1].Evaluate();

            if (firstParam is not string firstArg || secondParam is not string secondArg)
            {
                throw new FormatException();
            }

            args.Result = firstArg.EndsWith(secondArg, StringComparison.InvariantCulture);
        }
    }

``