Make object comparison to string invalid

Question

I'm using the Flee library to evaluate expressions that the users enters. I'm using the fact that expressions don't compile to warn the user of invalid input.

If I use an expression like var=="something" it will not compile if var is an int, because this is not valid code.

But if var is an object of a custom class I made it will compile (since the object has a ToString method I guess). How can I prevent the expression with the custom class from compiling if the variable that is contained in there can't be compared to string?

Update: here is an example piece of code that shows the problem. filter1 will throw an error when trying to compile with the message:

Ciloci.Flee.ExpressionCompileException: CompareElement: Operation 'Equal' is not defined for types 'Int32' and 'String'

But the second filter that using the custom class as variable type instead of the integer will not give an exception. But I want that custom class to behave like the int and not have an Equal operation defined. How to do that?

using System;
using Ciloci.Flee;

namespace FleeTest
{
    class VariableClass
    {
        // TODO
    }

    class Program
    {
        public static void Main(string[] args)
        {
            ExpressionContext context = new ExpressionContext();
            context.Options.ResultType = typeof(bool);

            VariableCollection var = context.Variables;
            var.ResolveVariableType += var_ResolveVariableType;

            string filter1 = "varInt=\"something\"";
            string filter2 = "varClass=\"something\"";

            try
            {
                IDynamicExpression e = context.CompileDynamic(filter1); 
            }
            catch(Exception e)
            {
                Console.WriteLine(e.Message);
            }

            try
            {
                IDynamicExpression e = context.CompileDynamic(filter2); 
            }
            catch(Exception e)
            {
                Console.WriteLine(e.Message);
            }

        }

        static void var_ResolveVariableType(object sender, ResolveVariableTypeEventArgs e)
        {
            if(e.VariableName == "varInt")
            {
                e.VariableType = typeof(int);
            }
            else if(e.VariableName == "varClass")
            {
                e.VariableType = typeof(VariableClass);
            }
        }
    }
}

Could you please come up with the actual code that you are using? — sujith karivelil, Dec 01 '16 at 06:33
If you think it's because of `ToString()` you can override it and throw an error inside. See if it works. — Emad, Dec 01 '16 at 06:34
I tried to throw an error in ToSting() indeed, but that didn't help. The error will only throw when running the code, not when it is parsed by the Flee library. I'll try to come with a minimum example that shows my problem. — Arno Gerretsen, Dec 04 '16 at 19:29
I have updated the question now with some example code that shows the problem I try to solve. — Arno Gerretsen, Dec 04 '16 at 19:47

score 0 · Answer 1 · answered Dec 01 '16 at 10:45

0

maybe try to convert your var like this:

  if(Convert.ToString(var) == "something")
  {
  //code
  }

I hope it's your probleme and it's help. Bye :)

answered Dec 01 '16 at 10:45

Clement Abergel

1
2

Make object comparison to string invalid

1 Answers1