eval(string) to C# code

Question

Is it possible to evaluate the following in C# at runtime

I have a class that contains 3 properties (Field,Operator,Value)

Answer 1

Disclaimer: I'm the owner of the project Eval Expression.NET

This library is close to being the JS Eval equivalent. You can almost evaluate and compile all the C# language.

Here is a simple example using your question, but the library goes way beyond this simple scenario.

int field = 2;
int value = 1;
string binaryOperator = ">";

string formula = "x " + binaryOperator + " y";

// For single evaluation
var value1 = Eval.Execute<bool>(formula, new { x = field, y = value });

// For many evaluation
var compiled = Eval.Compile<Func<int, int, bool>>(formula, "x", "y");
var value2 = compiled(field, value);

Answer 2

CSharpCodeProvider; switch statements that pick the proper different "operators"; the DLR... they are all ways you could do this; but they seem weird solutions to me.

How about just using delegates?

Assuming your Field and Value are numbers, declare something like this:

delegate bool MyOperationDelegate(decimal left, decimal right);
...
class Rule {
    decimal Field;
    decimal Value;
    MyOperationDelegate Operator;
}

Now you can define your 'rule' as, for example, a bunch of lambdas:

Rule rule1 = new Rule;
rule1.Operation = (decimal l, decimal r) => { return l > r; };
rule1.Field = ... 

You can make arrays of rules and apply them whichever way you wish.

IEnumerable<Rule> items = ...;

foreach(item in items)
{
    if (item.Operator(item.Field, item.Value))
    { /* do work */ }
}

If Field and Values are not numbers, or the type depends on the specific rule, you can use object instead of decimal, and with a little bit of casting you can make it all work.

That's not a final design; it's just to give you some ideas (for example, you would likely have the class evaluate the delegate on its own via a Check() method or something).