Expression Evaluator Void Returning Expressions

The ExpressionEvaluator library provides Eval() and ScopeCompile() functions which compile the expression into a Func<> delegate, and expects a return value. If expressions that return void such as code blocks are compiled as a Func<> will throw an exception.

To avoid this case, alternatively, you can call the Call() and ScopeCompileCall() methods to assume that the expression returns void and compiles the expression into an Action<> delegate.

Let's consider we have a simple class that contains one property and two void functions.

public class MyClass
{
    public int X { get; set; }
    public void Increment()
    {
        X++;
    }

    public void Increment(int value)
    {
        X += value;
    }
}

The following example shows how to compile the void functions using the Call() and ScopeCompileCall() methods.

public static void Example1()
{
    var data = new MyClass();

    var c1 = new CompiledExpression() { StringToParse = "X = 10" };
    var f1 = c1.ScopeCompileCall<MyClass>();
    Console.WriteLine(data.X);
    f1(data);
    Console.WriteLine(data.X);

    var reg = new TypeRegistry();
    reg.RegisterSymbol("data", data);
    var c1a = new CompiledExpression() { StringToParse = "data.Increment(5)", TypeRegistry = reg };
    Console.WriteLine(data.X);
    c1a.Call();
    Console.WriteLine(data.X);

    var c2 = new CompiledExpression() { StringToParse = "data.Increment()", TypeRegistry = reg };
    var f2 = c2.ScopeCompileCall();
    Console.WriteLine(data.X);
    f2(data);
    Console.WriteLine(data.X);
}

Now let's execute the above code and you will see the following output.

0
10
10
15
15
16